Lean Six Sigma

38 minute read

Lean Six Sigma Essential Glossary of Terms

Joseph Mapue

Joseph Mapue

When you combine the methods of Lean Manufacturing and Six Sigma’s data-driven approach to process improvement, you get a framework for excellence that truly moves the needle. Over the years, Lean Six Sigma implementation has demonstrated compelling ROI such that more than half of Fortune 500 companies have embraced the framework.

This Lean Six Sigma Glossary aims to provide students, professionals, and teams with an online dictionary that will enable them to quickly look up Lean Six Sigma terms and get a basic idea of what they are and their impact in process improvement and quality control. We hope you’ll find this resource useful!

Want to learn more about the Lean Six Sigma methodology?

Check out this ebook that will guide you through the key concepts of LSS.


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  • 5 Whys refers to a method of identifying the root cause (defect) of a problem by repeatedly asking “why” at least five times, with each answer serving as the platform for the next iterative Q&A until the actual defect or root cause is finally clear.    
  • 5S denotes a five-step process originally popularized in Japan that aims to organize a workplace for efficiency and effectivity. The five steps are Seiri (Sort), Seiton (Straighten), Seiso (Shine), Seiketsu (Standardize), and Shitsuke (Sustain).
  • 6 M’s identifies the six main elements that can cause variation in nearly all processes: Man, Machine, Material, Method, Measurement, and Mother Nature (The term is also rendered 5M1P to replace “man” with the more gender-agnostic “people”).
  • is the symbol for Six Sigma. The symbol “σ” is the lower case of the Greek letter Sigma (upper-case Σ), and is used in Statistics to denote standard deviation or to grade the maturity of a process. A process with a maturity of 6σ is said to produce defect-free products 99.99966% of the time.
  • 7 QC Tools (also Seven Basic Tools of Quality, 7 Quality Control Tools) refers to methods recommended by Japanese Engineering Professor Kauru Ishikagawa for process and quality improvement. These tools or techniques are: 1) Cause & Effect Diagrams, 2) Check Sheets, 3) Control Charts, 4) Histograms, 5) Pareto Charts, 6) Scatter Diagrams, and 7) Stratification Charts.
  • 8D is the shorthand for Eight Disciplines of Problem Solving, a collaborative and transparent framework for solving complex problems. The eight steps/disciplines are —
    D1: Create a Team,  D2: Describe the Problem,  D3: Develop a Containment Plan,  D4: Determine and Verify Root Causes,  D5: Verify Permanent Solution,  D6: Define and Implement Corrective Actions,  D7: Prevent Recurrence,  D8: Congratulate the Team.
  • 8 Wastes refer to the eight main types of actions, outcomes, or steps that are not required to satisfactorily complete a process or produce a desired output. The 8 wastes are summarized by the acronym DOWNTIME (Defects, Overproduction, Waiting, Non-utilized Talent, Transportation, Inventory Excess, Motion Waste, Excess Processing).


  • Accuracy refers to the degree of difference between actual and measured values.
  • An Action Plan is a simplified way of documenting tasks, task owners, methods, and task schedules associated with a project, campaign, or initiative.      
  • Affinity Charts are visuals created to organize large amounts of data based on their relationships (affinity, similarity). Also called Affinity Diagrams, affinity charts make it easier to understand complex problems by breaking them into smaller components and grouping similar or related components together.
  • Agile may refer to an adaptive, cross-functional, and customer-centric approach to software development/project management; or describe an organization whose processes, tools, and people readily adapt to changes while adequately managing costs and quality control.
  • The Alternative Path method generates alternative approaches to achieve the same outcome.
  • The Analyze Phase refers to the third stage in the DMAIC cycle, wherein a problem’s root cause(s) are identified.
  • Andon is a Japanese manufacturing term that denotes an alert communication or signaling system for facilitating rapid response to problems in a system or process.
  • ANOVA is the acronym for Analysis of Variance, a type of statistical test for determining whether there are significant differences between two groups of data.  
  • An Approval is a common step in many kinds of processes, which requires time for review and sign-off. The more time it takes to earn approval, the slower the process becomes.
  • Attribute Data may refer to 1) a binary-type data (aka Qualitative Data) whose value can only be one of two possibilities (e.g., yes/no, true/false, pass/fail, etc.); or 2) a type of data (aka Discrete Data) whose possible values are restricted to whole numbers such as the number of defects, users, or complete cycles.
  • Autonomation (aka Jidoka) refers to a class of “smart” automation that deactivates itself or halts a process when specific, abnormal conditions occur, thereby allowing workers to investigate and solve the problem. Invented by Sakichi Toyoda in the 19th century, the concept became one of the pillars of Toyota’s production system. Autonomation consists of 4 steps:  1) Detect the anomaly; 2) Stop the process/machine; 3) Fix the anomaly; and 4) Investigate the root cause and implement a countermeasure.
  • Average (aka Mean) refers to the mathematical result when the sum of a set of values is divided by the number of elements in the set.


  • Bartlett’s Test is a statistical method for finding significant differences among the variances of two or more data sets, with the aim of identifying the root cause(s) of a problem.  
  • Bias describes the tilt, leaning, or tendency of a measured value as compared to the actual value. When present (i.e., measured value is not equal to actual value), bias is either positive or negative.
  • A Black Belt refers to the second highest competency level for Six Sigma practitioners and describes a person who has achieved such competency. Six Sigma Black Belts are full-time team leaders tasked to solve problems.
  • A Bottleneck is a point in the process where the normal or acceptable flow is impeded due to abnormally high volume or limited capacity of the system to process such volume.
  • A Box Plot or Whisker Plot is a way of visualizing a data set into four parts or quartiles.
  • Breakeven Analysis is an accounting method for determining the minimum number of units or subscriptions to sell in order to cover total costs.   
  • A Business Case is a term denoting a rationale or justification for a particular action, decision, product, or service.


  • C-Chart are visualizations of data groups used in tracking defects.
  • CAPA is the acronym for Corrective Action and Preventive Action
  • A Cause-And-Effect Diagram is a visual representation of all variables (causes, factors, etc.) that can affect a certain quantity (output, problem, etc.). The resulting image usually resembles a fish, hence the alternative term Fishbone Diagram. It is also sometimes called Ishikawa Diagram after its creator.  
  • Change Management refers to the actions, methods, and processes designed to support people and teams as they undergo organizational change.
  • Common Cause Variation refers to a class of variation that is natural, predictable, or inherent in a system.
  • A Control Chart is a tool used in statistical process control, consisting of a center line and statistically determined upper and lower control limits.
  • Continuous Data is a class of data that can have any value, unlike discrete data that can only have whole numbers.
  • Continuous Improvement refers to a mindset, actions, or efforts to improve an organization’s processes and products.
  • Correlation Coefficient is a measure of the relationship between two variables.  
  • Cost of Poor Quality (COPQ) refers to unnecessary expenses (such as process delays, product recalls, rework, and warranty costs) incurred by the organization due to process inefficiencies or product defects.
  • A Countermeasure is a plan or action aimed at addressing an issue even on a temporary basis.
  • Cp is the statistical symbol for Process Capability calculated as the ratio of tolerance over process variance.    
  • Critical-to-Quality (CTQ) describes any quantity, element, attribute, or factor that impacts the quality of a product or system.     
  • Critical X is a process or system input that has a significant influence on one or more outputs of the system/process.
  • A Cross-Functional Map is a lane-based diagram that correlates functions and stakeholders (team, or individual) to demonstrate how the entire process moves across departments and functions from start to finish. Also called a Swimlane or Deployment Map.
  • Customer refers to anyone who uses an organization’s product or service.
  • Cycle Time refers to the total time that has elapsed from process start to process completion.


  • A Defect refers to any output of a process that fails to meet a pre-defined standard, requirement, or specification such as color, quantity, dimensions, temperature, performance speed, etc. Any product or service that has at least one defect is described as Defective.
  • Defect Opportunity refers to any event or instance where a substandard output (defect) can occur.
  • The Define Phase of the DMAIC method involves clearly and precisely defining the problems, customer requirements, opportunities, scope, and improvement goals of a project or initiative.
  • DFSS (Design for Six Sigma) is the application of Lean Six Sigma principles in the field of product/service design for the purpose of improving performance, managing costs, and optimizing value.
  • Discrete Data refers to quantities whose values can only be whole numbers (such as the number of defects). In contrast, Variable/Continuous data such as velocity, weight, and distance can have any numerical value.  
  • DMADV is the acronym for Define, Measure, Analyze, Design, and Verify, the Lean Six Sigma method for designing new processes and products.
  • DMAIC is the acronym for Define, Measure, Analyze, Improve and Control, the five key phases of the Lean Six Sigma framework used in solving business and process problems.  
  • DOWNTIME (Defects, Overproduction, Waiting, Non-utilized Talent, Transportation, Inventory Excess, Motion Waste, Excess Processing) is the acronym for the 8 types of wastes in the Lean Manufacturing/Enterprise framework.  
  • DPMO (Defects per Million Opportunities) is a key Six Sigma metric that refers to the total number of observed defects per one million defect opportunities.
  • DPU (Defects per Unit) is the total number of observed defects in a specific class of units divided by the total number of those units.


  • Error Proofing refers to any method, mechanism, or device in a process that helps eliminate defects through detection, prevention, or correction. Also called Mistake Proofing (Poka Yoke) as coined by Quality Control and Lean Manufacturing pioneer Shigeo Shingo.
  • Error-Proofing Methods refer to the main approaches to error control as recommended by Shigeo Shingo: Elimination, Flagging, Facilitation, Mitigation.
  • Effectiveness describes how well a process output meets desired specifications or satisfies customers’ expectations.
  • Extra-Processing is a form of waste that describes the process of adding extra features or producing an output beyond customer requirements or quality standards.
  • External Failure occurs when defective items pass through the process and reach customers, leading to customer dissatisfaction.


  • A Facilitator is an intermediary who drives collaboration among all participants in a process improvement project, effort, or initiative.   
  • FMEA (Failure Modes and Effect Analysis) is a risk management tool for analyzing potential failures in terms of occurrence, severity, and detection.
  • Force Field Analysis refers to a brainstorming method similar to building a Pros and Cons table where all factors that either support or oppose an idea are gathered, weighed, and analyzed.  
  • Four Absolutes of Quality Management refer to four key attributes of quality as conceptualized by Philip Crosby:
    1. Quality means conformance to requirements
    2. Quality comes from prevention
    3. Quality performance standard has zero defects
    4. Quality measurement is the price of non-conformance
  • A Future State Map is a plan that visually charts the desired state (zero waste) for a given process.   


  • Gage R&R (Repeatability and Reproducibility) is a test for analyzing a measurement system’s level of variation compared to the total variation of the process.    
  • A Gallery Walk is a space where successful Lean Six Sigma projects or improvement ideas are formally showcased to educate a wider audience. It is sometimes called a Solution Parking Lot.
  • Gemba is the Japanese term for ‘real place” which signifies a space where actual work happens.  
  • A Goal Statement defines the desired outcomes of a process improvement effort.
  • A Green Belt refers to a Six Sigma competency level and describes a person who has received approximately two weeks training in DMAIC. Six Sigma Green Belts perform part-time support duties and generally handle smaller-scoped projects.


  • A Handoff refers to any transition point where control/management of products or certain aspects of the process changes ownership (i.e., hands).
  • Help-Hinder is a method for identifying operational or workflow issues within a team. The approach requires each member to cite the instances where they help facilitate (help) the process as well as the instances where they tend to slow (hinder) the group. The aim is to synergize the team for optimum efficiency.
  • Hidden Factory (also Hidden Plant or Hidden Operation) refers to the phenomenon coined by Quality Control pioneer Armand Feigenbaum where untracked waste (time, effort, opportunity, materials, etc) in manufacturing plants accumulates due to extra corrective work needed to fix defects (things that should have been done right the first time).   
  • A Histogram is a bar chart that shows the frequency distribution of a given data set.
  • Historical Parameters are baseline data used in tracking progress, measuring change, or comparing an original system state to a new one
  • Huddle Meetings are daily short meetings (around 15 minutes) designed for team coordination. Huddles require the sharing of relevant reports.  
  • A Hypothesis Statement is a reasonable conjecture that identifies or describes a possible cause(s) of defects in the process.  
  • Hypothesis Testing refers to the process of verifying whether an assumption or statement about a data set is true.  


  • An I-MR Chart (Individual and Moving Range Chart) tracks averages and variation in a process. The I portion detects data trends and shifts, while the MR component shows short-term variability.
  • Implementation Team refers to a cross-functional group tasked to drive Lean Six Sigma implementation by defining, documenting, and executing policies, processes, and methods aimed at eliminating defects.
  • The Improve Phase of the DMAIC method identifies opportunities for improvements based on information discovered in prior stages.
  • Improvement Kata is a method for developing positive behavioral change that facilitates actual transition from a current state to a desired state. Also called Improvement Routine.
  • An Input is a resource utilized in a system or process.
  • Inspections are processes that probe a process or product for defects. The goal of Lean Six Sigma is to mistake-proof processes to eliminate the need for inspections and reworks.  
  • Institutionalization refers to the process of rendering process improvements permanent by achieving procedural, behavioral, and cultural change.
  • Internal Failure refers to any defect that has been identified and fixed before reaching a customer.   
  • Inventory refers to materials and units that remain undelivered or unutilized for a given period. Inventory excess, which hinders capital flow and uses valuable space, is considered a major waste.


  • Jidoka is a Japanese term that describes a class of “smart” automation capable of deactivating itself or halting a process when specific, abnormal conditions occur. The action allows human workers to investigate and solve the problem (also known as Autonomation).
  • Just-In-Time (JIT) describes a system or method for delivering the right items in the right place at the right time and in the right measures.


  • Kaizen is a Japanese term combining the concepts of change (kai) and goodness (zen). In the corporate world, it has come to mean “continuous improvement.”
  • A Kanban Board (from “signpost” in Japanese) is used to visually represent and track tasks and workflows to facilitate optimum collaboration.
  • A Kano Model is a diagram that shows what customers receive in terms of a) basic features, b) performance items, and c) “delighters.”


  • Lead Time refers to the period from the time an order is placed to the moment the order is delivered.
  • Lean is a framework for waste elimination in manufacturing, software development, enterprise management, and other processes. Much of the Lean model originated from Toyota’s production system. Leaders in an organization with a Lean culture fully support process improvements while workers are expected to directly help fix systemic problems they encounter in their workflow.   
  • Lean Six Sigma combines the aims and principles of the Lean framework (zero waste) and the Six Sigma model (high system predictability, minimum variation). Lean Six Sigma advocates continuous improvement and implements the DMAIC approach to effecting organizational change.
  • Linearity is the variation (consistency of bias) between a known standard or “baseline truth” across the full range of expected values.  
  • Lower Control Limit is the lower limit — usually three standard deviations below average — above which a process is said to be in control.  
  • Lower Specification Limit refers to the lower limit set for a product, property or attribute, below which is considered unacceptable.


  • Master Black Belt is the highest Lean Six Sigma competency level, or a person who has earned such competency. Master Black Belts provide leadership, support, and mentorship to other Belts.  
  • Measurement System Analysis is a way of assessing the precision and accuracy of specific measurement methods. Also called MSA or Gage R&R.     
  • The Median is the number, quantity, or value at the midpoint of a data frequency distribution.    
  • Moment of Truth describes the event when a customer forms an opinion about a process he or she is interacting with.
  • MoSCoW is an acronym for “Must have, Should have, Could have, Would have,” a means of classifying features in terms of importance or priority.  
  • Motion Waste is the unnecessary movement of business inputs that do not add value and can be eliminated when the process is optimized. Motion waste is counted among the 8 major wastes (DOWNTIME).  
  • Muda is the Japanese term for “waste,” which can be anything in the process or product that does not add value from customers’ vantage point.


  • “n” commonly stands for the number of data in statistical formulas and calculations.
  • “N” commonly stands for populations in statistical computations.
  • Non-Utilized Talent is an unwanted waste counted among the 8 Wastes in Lean Manufacturing.
  • Non-Value Adding Activities are process steps that typically exemplify any of the 7 wastes in the Lean Six Sigma framework. These include rework, unnecessary movement, and others. Non-value adding activities increase business costs and often prolong production time.       
  • Normal Distribution refers to a statistical distribution characterized by a gentle bell-shaped curve.
  • A Normality Test is used to verify if a sample conforms to a normal distribution.    
  • An nP Chart monitors the proportion of defective items in consistently-sized data sets.


  • An Operational Definition is a clear description of an item or quantity as well as the process and parameters within which it is to be collected, measured, or used.
  • An Output is an item, characteristic, or resource produced by a process or system.
  • Overproduction is considered a major waste in the Lean Manufacturing framework.


  • A P Chart is used for tracking the fraction of units with defects in a given set of discrete data.
  • A Pareto Chart is a diagram that displays the frequency of occurrences (as a bar chart) and the total percentage of occurrences (as a line graph). In the Lean Six Sigma environment, the occurrences refers to defects or defective units.
  • The Pareto Principle posits that a large share of outcomes are caused by a small set of factors. Named after the Italian economist Vilfredo Pareto, the principle is also called the 80/20 rule, where 80% of outcomes are caused by just 20% of causes.
  • PDCA is a problem-solving technique that stands for Plan, Do, Check, and Act. It is also rendered as PDSA (Plan Do Study Act).
  • Perfection refers to the iterative process of continuous improvement advocated by Lean Six Sigma and related frameworks.
  • A Pilot refers to an initial and limited deployment of a Lean Sigma Six solution for the purpose of verifying its effectivity in solving a problem. Pilots are during the Improve phase to validate the root cause hypotheses without incurring excessive risks and cost.
  • Poka-Yoke is Japanese for “error-proof.” In the Lean Six Sigma environment, poka-yoke means to mistake-proof the process in order to eliminate defects, largely by preventing human errors or establishing reliable alarm systems that send out a warning whenever a potentially defect-causing factor emerges.
  • Process Cycle Efficiency is a metric used to prioritize improvement opportunities and is computed by dividing the value-added time of process with its total lead time.
  • Process Improvement is the overriding goal of Lean Six Sigma and entails continuous, iterative, and incremental reduction of errors, wastes, defects, and costs.
  • A Project Charter outlines key details, goals, intentions, and many other essential components of your project like a roadmap. It’s also used as a contract between the team implementing the project and the person funding it, known as the sponsor.
  • Project Y is the key output of the process that is being improved.  
  • Proportion Defective is expressed as a percentage and denotes the proportion of defective units in a total population.


  • QDIP is an acronym for Quality, Delivery, Inventory, and Productivity.
  • Quality is metric that describes whether a product, process, or system satisfies customer expectations or meets their requirements.
  • QFD is an acronym for Quality Function Deployment, a process for integrating customer requirements across all aspects of product design and delivery.
  • A Quartile is 25% of a data set that has been subdivided into four. Quartiles are used to study trends, rank performance, or identify causes that improve or degrade process efficiencies.  

Want to learn more about the Lean Six Sigma methodology?

Check out this ebook that will guide you through the key concepts of LSS.


  • R&R is an acronym for repeatability and reproducibility, the two key metrics that are tested during a measurement systems analysis.
  • RACI is a matrix used in strengthening accountability for different aspects of a project. It stands for Responsible, Accountable, Consulted, and Informed.
  • Range refers to the “spread” of a data set, calculated by getting the difference between the set’s highest and lowest values.   
  • Repeatability describes a measurement scenario where a single person gets the same results for every measurement session.
  • Reproducibility describes a measurement scenario where multiple persons get the same results every time.
  • Rework refers to the effort and associated resources required to fix a process or products defect.
  • Rolled Throughput Yield is a metric that indicates the percentage of units that pass through a process without defects.
  • Root Cause Analysis is a technique for identifying the “root cause” of a process problem.
  • Root Cause Hypothesis is a well-thought-out guess identifying the (potential) root cause of a problem. It is part of the Analyze Phase in the DMAIC framework.    
  • RPN is an acronym for Risk Priority Number, a cumulative failure rating or score that covers frequency of occurrence, detectability, and severity.
  • RUMBA describes a set of criteria for validating customer requirements and stands for Reasonable, Understandable, Measurable, Believable and Achievable.


  • s (or sd) stands for standard deviation, a measure that quantifies the degree of variation or dispersion of a data set.
  • Seven Basic Tools of Quality refers to Lean Six Sigma tools recommended by Kaoru Ishikawa for their relative simplicity compared to other statistical techniques. These tools are: 1) Fishbone diagram, 2) Check Sheet, 3) Control Chart, 4) Histogram, 5) Pareto Chart, 6) Scatter Diagram, and 7) Flow Chart/Stratification.
  • Sigma Score refers to a statistical measure of process capability. It is expressed as the number of standard deviations (sigma level) between a process’ center and the closest specification limit. The Sigma Score is also rendered as Z.
  • SIPOC is an acronym for Suppliers, Inputs, Process, Outputs, and Customers, representing a top-view of a fairly common business process. It is sometimes rendered as COPIS.
  • Six Sigma is a framework that provides organizations with data-driven tools, techniques, and strategies for process improvement. By reducing defects and variability, Six Sigma aims to drive process performance and enhance output quality.
  • Six Sigma Implementation Roles refer to a system of responsibilities Six Sigma practitioners assume as agents of organizational change and leaders of specific process improvement initiatives. These roles are linked to the framework’s belt-based competency system. The framework implements the following roles: 1) Six Sigma Deployment Leader, 2) Six Sigma Champion, 3) Six Sigma Master Black Belt , 4) Six Sigma Black Belt, 5), Six Sigma Green Belt, 6) Six Sigma Yellow Belt, and 7) Six Sigma White Belt (beginner level).
  • A Solution Parking Lot is a space for highlighting improvement ideas and accomplishments throughout the lifecycle of a Lean Six Sigma project. It is also called a Gallery Walk.   
  • A Special Cause Variation is a type of process variation that is non-random but irregularly occurring, which erodes process predictability.
  • SQDC is an acronym for Safety, Quality, Delivery, Cost.
  • Stability refers to the characteristic of a process that describes whether it exhibits any special cause variation or any pattern of change.
  • Standard Deviation is a statistical value that shows the average level data values vary relative to the mean.
  • Stratification is a method used to analyze data where values are grouped into different strata or layers.


  • The Taguchi Loss Function is a statistical concept developed by Genichi Taguchi to describe the relationships between quality, variance, and customer dissatisfaction (loss). According to Taguchi, quality loss follows a parabolic curve, meaning the drop in quality does not happen suddenly from the customer’s view but depends on how much a product varies from the customer’s expectation.
  • The Taguchi Methods refer to Genichi Taguchi’s framework on quality control that aims to meet customer expectation by reducing process variation and costs. The framework prescribes several statistical methods including those for system design, testing, and tolerance.
  • Takt Time is a German term that refers to the required rate/pace of production to meet customer demand. It is not the completion period for one unit but the average time from the point at which one unit has been completed to the point at which the next unit has been completed.
  • TOC is an acronym for Theory of Constraints, which adopts the mantra, “a chain is only as strong as its weakest link” to the field of organizations and processes. The theory was introduced by Eliyahu M. Goldratt and was embraced by proponents of process improvement, project management, and organizational change.
  • The Toyota Production System is a template appropriated by Lean Manufacturing advocates for reducing process waste and conserving resources. It espouses the practices of identifying root causes to solve problems, and of preventing overproduction. Also called by its acronym TPS.
  • TQM is an acronym for Total Quality Management, a method developed in the 1980s for cultivating a culture of continuous improvement in organizations.
  • Transportation — in the Lean Six Sigma ecosystem — is one of the 8 wastes of production. It refers to the practice of moving products across different touch points in the process as it flows from start to product completion. Some touch points and moves are unnecessary and only add to waste.
  • Trend refers to a value’s systemic and biased change relative to a variable such as time.
  • Trimmed Mean is the resulting mean value of a data set, sample, or population where outliers have been removed.  
  • TSSW  is the acronym for Thinking the Six Sigma Way, a work mindset that promotes continuous improvement and the application of Lean Six Sigma principles in solving both simple and complex business problems.  


  • A u-chart is a diagram that shows how a process changes over time, depicted in terms of the number of defects that occur in a sample or data set.
  • Upper Control Limit is the upper limit — usually three standard deviations above average — below which a process is said to be in control. Also known by its acronym UCL.
  • Upper Specification Limit refers to the upper limit set for a product, property or attribute, above which is considered unacceptable.
  • Upstream is a directional term for describing activities, touch points, and processes that chronologically precedes a given process or item.


  • Value-Adding Activities are defect-free process steps that are required to complete a product or service in line with customer expectations.
  • Value Analysis refers to the process of classifying process steps or activities into three categories:
    1. Value-Adding Activities
    2. Non-Value Adding Activities
    3. Value-Enabling Activities    
  • Value-Enabling Activities are process steps that are required (such as regulatory compliance) but do not directly add value to the product as viewed from a customer’s perspective.
  • Variability refers to the property of an item, system, or process to assume or exhibit different values.
  • Variance is a measure of variability in a data set. In statistical equations, variance is the square of standard deviation.
  • Variation is the consistency of an output or data set. Lean Six Sigma aims to reduce variation and increase predictability in processes.
  • Voice of the Business (VOB) refers to the priorities of the organization, including profitability and revenue.  
  • Voice of the Customer (VOC) refers to the needs and desires of customers, including product features, service requirements, and customer expectations.
  • Voice of the Process (VOP) refers to the ability of a process to meet business and customer needs. VOP is often rendered as an efficiency-related metric.


  • Waiting is one of the 8 Wastes in Lean Six Sigma. Waiting occurs when a person or a team cannot proceed with their work because they are still waiting for a required activity, approval, item, or information from another person or unit.
  • White Belt refers to a Lean Six Sigma competency level, or a person who has earned such competency. Representing the beginner role in the system, white belts understand fundamental Lean Six Sigma concepts such as the 8 Wastes and DMAIC.
  • Work in Process (WIP) may refer to inventories, queued parts, and other pending items waiting to be worked on towards completion.


  • The variable x is used in Lean Six Sigma as part of the expression Y=f(x), where Y is the output and x the input.
  • An X-Bar (x) stands for the sample mean statistics.
  • X-Bar & R Charts are control charts that are used to verify whether a process is stable and predictable. The “R in the term stands for “range.”
  • X-Bar & S (standard deviation) Charts are control charts that are used to track process variability. The “s” in the term stands for “standard deviation.”


  • The variable Y is used in Lean Six Sigma as part of the expression Y=f(x), where Y is the output and x the input.
  • Yellow Belt refers to a Lean Six Sigma competency level and describes a person who has achieved such competency. Yellow Belts understand the fundamentals of Lean Six Sigma methodologies and are able to support process improvement projects.   
  • Yield is the value indicating the percentage of good output generated by a process.  


  • The statistical symbol Z stands for Sigma score, a measure of process capability.
  • Zero Defects refers to a conceptual goal coined by Quality Control pioneer Philip Crosby who advised businesses to do things right the first time.
  • Zero Quality Control is a method that aims to eliminate the likelihood of human error, thereby eliminating the need for inspection, which is considered a wasteful activity.


  • ANOVA. Analysis of Variance.  
  • CAPA. Corrective Action and Preventive Action.
  • COPQ. Cost of Poor Quality.   
  • CTQ. Critical-to-Quality.
  • DFSS. Design for Six Sigma.
  • DMADV. Define, Measure, Analyze, Design, and Verify.
  • DMAIC. Define, Measure, Analyze, Improve and Control.  
  • DOWNTIME. Defects, Overproduction, Waiting, Non-utilized Talent, Transportation, Inventory Excess, Motion Waste, Excess Processing.  
  • DPMO. Defects per Million Opportunities.
  • DPU. Defects per Unit.
  • FMEA. Failure Modes and Effect Analysis.
  • JIT. Just-In-Time.
  • LCL. Lower Control Limit.
  • MoSCoW. Must have, Should have, Could have, Would have. 
  • PDCA. Plan, Do, Check, and Act.
  • PDSA. Plan Do Study Act.
  • QDIP. Quality, Delivery, Inventory, and Productivity.
  • QFD. Quality Function Deployment.
  • R&R. Repeatability and Reproducibility.
  • RACI. Responsible, Accountable, Consulted, and Informed.
  • RPN. Risk Priority Number.
  • RUMBA. Reasonable, Understandable, Measurable, Believable and Achievable.
  • SIPOC. Suppliers, Inputs, Process, Outputs, and Customers    
  • SQDC. Safety, Quality, Delivery, Cost. 
  • TOC. Theory of Constraints.
  • TPS. Toyota Production System.
  • TQM. Total Quality Management.
  • TSSW. Thinking the Six Sigma Way.  
  • UCL. Upper Control Limit.
  • VOB. Voice of the Business.
  • VOC. Voice of the Customer.
  • VOP. Voice of the Process.


  • stands for Six Sigma.
  • Cp is the statistical symbol for Process Capability calculated as the ratio of tolerance over process variance.
  • µ (pronounced miyu) typically represent population mean in Statistics.
  • N often symbolizes a population
  • n represents the number of data in a sample
  • s (or sd) stands for standard deviation.
  • σ (sigma) represents the actual standard deviation of a given population
  • x commonly represents one data value
  • x is the symbol for X Bar.

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Joseph Mapue

Joseph Mapue

Joseph Mapue wears his writer's hat wherever he goes, crafting top-notch content on business, technology, creativity, and innovation. He is also a dreamer, builder, father, and gamer.