Six Sigma Glossary: Understanding Process Improvement
- Michelle M
- 3 days ago
- 6 min read
Six Sigma has become one of the most widely adopted methodologies for process improvement, operational excellence, and quality management. At its core, Six Sigma uses data-driven decision-making, statistical tools, and structured approaches to minimize variation and eliminate defects in processes. But for newcomers, or even experienced practitioners, the terminology can sometimes feel overwhelming.
That’s why a Six Sigma Glossary is so valuable. It provides clarity on the hundreds of terms, tools, and techniques used in the methodology. Whether you’re a project manager, a Green Belt, a Black Belt, or simply someone looking to understand how Six Sigma works, this glossary will help you navigate the language of quality improvement.
Below are 100 essential Six Sigma glossary items, each explained in detail to give you a comprehensive understanding of the concepts and principles that drive this methodology.
DMAIC
The core problem-solving methodology in Six Sigma, standing for Define, Measure, Analyze, Improve, and Control. It provides a structured approach to process improvement and is widely used for reducing variation and defects.
DMADV
Another methodology within Six Sigma that stands for Define, Measure, Analyze, Design, and Verify. It is used in Design for Six Sigma (DFSS) to create new processes or products that meet customer expectations from the start.
Defect
Any instance in which a product or process fails to meet customer requirements. Reducing defects to near zero is the fundamental aim of Six Sigma.
DPMO (Defects Per Million Opportunities)
A measure of process performance that indicates the number of defects per one million opportunities. It is a key metric for calculating Sigma level.
Sigma Level
A measure of process capability that reflects how well a process performs in terms of producing defects. Higher Sigma levels indicate fewer defects.
Critical to Quality (CTQ)
Key measurable characteristics of a product or process that are essential to meeting customer requirements. CTQs are identified early in a project to ensure focus on what matters most.
Process Capability
The ability of a process to consistently produce outputs within specified limits. It is measured by indices such as Cp and Cpk.
Cp
A capability index that measures a process’s potential to produce outputs within specifications, without considering process centering.
Cpk
A capability index that considers both the process variability and its centering relative to specification limits. A higher Cpk indicates better performance.
Voice of the Customer (VOC)
The needs, expectations, and preferences expressed by customers. VOC is gathered through surveys, interviews, or feedback mechanisms to guide improvement efforts.
Voice of the Process (VOP)
The actual performance of a process, typically measured through data collection and analysis. Comparing VOC and VOP highlights gaps to be closed.
Control Chart
A statistical tool used to monitor process stability over time. It shows whether variations are due to common causes or special causes.
Histogram
A graphical representation of data distribution that helps visualize variability and identify patterns within a process.
Pareto Chart
A bar graph that displays data in descending order of frequency or impact, often used to identify the "vital few" causes in line with the Pareto principle.
Fishbone Diagram (Ishikawa)
A cause-and-effect diagram used to systematically identify root causes of a problem. It organizes causes into categories like people, process, equipment, and environment.
Root Cause Analysis
The practice of investigating and identifying the underlying reasons for defects or problems, rather than addressing symptoms.
Kaizen
A philosophy of continuous improvement through small, incremental changes. Often used in Lean Six Sigma to improve efficiency and reduce waste.
Kaizen Event
A short, focused improvement workshop where teams work intensively to identify and implement process improvements.
Lean Six Sigma
A methodology that combines Lean principles (waste elimination) with Six Sigma principles (variation reduction) for overall process excellence.
Waste (Muda)
Any activity that does not add value to the customer. Lean principles identify seven types of waste, such as overproduction, waiting, or defects.
SIPOC Diagram
A high-level process map showing Suppliers, Inputs, Process, Outputs, and Customers. It helps clarify scope and boundaries at the start of a project.
FMEA (Failure Modes and Effects Analysis)
A structured tool for identifying potential failure modes in a process, assessing their severity, likelihood, and detectability, and prioritizing corrective actions.
Risk Priority Number (RPN)
A score used in FMEA calculated by multiplying severity, occurrence, and detection ratings. Higher RPNs indicate higher priority risks.
Measurement System Analysis (MSA)
A method used to evaluate the accuracy and reliability of measurement systems, ensuring that collected data can be trusted.
Gage R&R
Part of MSA, this analysis evaluates the repeatability and reproducibility of measurement tools and operators.
Hypothesis Testing
A statistical method used to make inferences about populations based on sample data. It helps validate assumptions in Six Sigma projects.
p-Value
A probability value that helps determine whether an observed effect is statistically significant. A low p-value suggests rejecting the null hypothesis.
Confidence Interval
A range of values within which the true population parameter is expected to lie, with a given level of confidence.
Regression Analysis
A statistical technique used to model relationships between variables and predict outcomes. It helps identify which factors significantly impact a process.
Correlation Coefficient
A measure of the strength and direction of the relationship between two variables. Values range from -1 to +1.
Scatter Plot
A graphical representation of two variables plotted on a Cartesian plane to identify potential relationships or trends.
Control Plan
A documented strategy that describes how a process will be controlled to maintain improvements after a Six Sigma project.
Standard Operating Procedure (SOP)
A set of step-by-step instructions that ensure processes are performed consistently and correctly.
Project Charter
A document that formally defines a Six Sigma project’s scope, objectives, team, and timeline. It provides direction and alignment for the project.
Black Belt
A Six Sigma expert who leads improvement projects, mentors Green Belts, and applies advanced statistical tools.
Green Belt
A Six Sigma practitioner trained to support projects, often part-time, while performing their regular job duties.
Yellow Belt
An entry-level Six Sigma practitioner with basic knowledge of the methodology who supports larger projects.
Master Black Belt
An experienced Six Sigma professional who trains, coaches, and mentors Black Belts and Green Belts while overseeing program deployment.
Champion
A senior leader who sponsors Six Sigma projects, removes barriers, and ensures alignment with organizational goals.
Process Owner
The individual responsible for a process’s performance and sustainability after improvements have been implemented.
Project Sponsor
An executive who authorizes, funds, and supports a Six Sigma project, ensuring resources and organizational alignment.
CTQ Tree
A diagram that translates broad customer needs into specific, measurable requirements. It ensures alignment between VOC and process outputs.
Balanced Scorecard
A performance management tool that measures financial and non-financial metrics to provide a holistic view of organizational performance.
Normal Distribution
A probability distribution shaped like a bell curve, commonly used in Six Sigma for statistical analysis.
Standard Deviation
A measure of variability in data. Lower standard deviation indicates less variation in process performance.
Z-Score
A measure that indicates how many standard deviations a data point is from the mean. Useful in defect analysis.
DOE (Design of Experiments)
A statistical method for systematically planning and conducting experiments to determine cause-and-effect relationships between variables.
ANOVA (Analysis of Variance)
A statistical technique used to compare means across multiple groups to determine if significant differences exist.
Process Mapping
The visual representation of a process, often through flowcharts, to analyze and improve efficiency.
Swimlane Diagram
A type of process map that divides activities by function or role, making responsibilities clearer.
Benchmarking
The practice of comparing processes, metrics, or practices against industry leaders to identify improvement opportunities.
Value Stream Mapping
A Lean tool that maps the flow of materials and information, highlighting waste and improvement opportunities.
Conclusion - Six Sigma Glossary: Understanding Process Improvement
A strong understanding of Six Sigma terminology is critical for anyone engaged in process improvement. This Six Sigma Glossary equips professionals with the language and knowledge they need to effectively collaborate, analyze, and implement meaningful changes. Mastery of these terms creates a foundation for continuous improvement and ensures teams can speak the same language when striving toward operational excellence.
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