Six Sigma Glossary: Complete Terms and Definitions

Essential Six Sigma Terms and Concepts

Understanding Six Sigma terminology is fundamental to effective application of the methodology. This glossary covers everything from basic concepts to advanced statistical terms used by practitioners at all levels.

Professional Six Sigma training from Eastman Business Institute ensures proper understanding and application of these concepts in real-world scenarios.

Core Six Sigma Definitions

Six Sigma Fundamentals

Six Sigma

A data-driven methodology for eliminating defects by reducing process variation to achieve 99.99966% defect-free performance (3.4 defects per million opportunities).

DMAIC

The five-phase Six Sigma methodology: Define, Measure, Analyze, Improve, Control. Used for improving existing processes. See our complete DMAIC guide.

DFSS (Design for Six Sigma)

Six Sigma methodology applied to new product development and process design, typically following DMADV (Define, Measure, Analyze, Design, Verify) framework.

Sigma Level

A measure of process capability expressed in standard deviations. Higher sigma levels indicate better performance and fewer defects.

DPMO (Defects Per Million Opportunities)

A standardized metric for measuring process performance regardless of complexity. See our detailed explanation of DPMO calculation.

Process Capability Terms

Cpk (Process Capability Index)

A statistical measure that quantifies how well a process performs relative to its specification limits, accounting for both variation and centering.

Cp (Process Capability Ratio)

The ratio of specification width to process width, assuming the process is centered. Cp = (USL - LSL) / (6σ).

Process Capability

The ability of a process to consistently produce output within specification limits. Measured using indices like Cp, Cpk, Pp, and Ppk.

USL (Upper Specification Limit)

The maximum acceptable value for a process characteristic as defined by customer requirements or engineering specifications.

LSL (Lower Specification Limit)

The minimum acceptable value for a process characteristic as defined by customer requirements or engineering specifications.

Six Sigma Belt Levels and Roles

Certification Levels

White Belt

Entry-level Six Sigma knowledge focusing on basic concepts and terminology. White Belts participate in improvement projects as team members.

Yellow Belt

Basic problem-solving skills and understanding of Six Sigma tools. Yellow Belts lead small improvement projects and support larger initiatives.

Green Belt

Intermediate-level Six Sigma expertise. Green Belts lead improvement projects part-time while maintaining regular job responsibilities.

Black Belt

Advanced Six Sigma expertise with full-time commitment to process improvement. Black Belts lead complex projects and mentor Green Belts.

Master Black Belt

Highest level of Six Sigma expertise focusing on organizational deployment, training development, and strategic guidance.

Champion

Executive-level sponsor who provides strategic support and removes organizational barriers for Six Sigma projects.

Statistical and Quality Terms

Statistical Concepts

Standard Deviation (σ)

A measure of process variation that quantifies how spread out data points are from the process mean.

Process Mean (μ)

The average value of a process output over time, representing the central tendency of the process.

Control Limits

Statistical boundaries on control charts that distinguish between common cause and special cause variation. See our control chart guide.

Common Cause Variation

Natural, inherent variation in a process that is predictable and stable over time.

Special Cause Variation

Variation caused by specific, identifiable factors that are not part of normal process operation.

Statistical Process Control (SPC)

The use of statistical methods to monitor and control process performance. Learn more about SPC implementation.

Quality Tools and Techniques

Pareto Chart

A bar chart that ranks problems or causes in descending order of frequency, based on the 80/20 principle. See our Pareto analysis guide.

Fishbone Diagram

A cause-and-effect diagram that systematically identifies potential causes of a problem. Also called Ishikawa diagram.

FMEA (Failure Mode and Effects Analysis)

A systematic method for identifying potential failures and their effects, used for risk assessment and prevention.

Root Cause Analysis

Systematic investigation to identify the fundamental cause of a problem. Learn various root cause analysis techniques.

5 Whys

A simple but effective root cause analysis technique that asks "why" five times to drill down to underlying causes.

Lean and Process Improvement Terms

Lean Methodology

Kaizen

Japanese philosophy of continuous improvement through small, incremental changes involving all employees.

5S

Workplace organization methodology: Sort, Set in Order, Shine, Standardize, Sustain.

Value Stream Mapping

Visual tool that maps the flow of materials and information through a process to identify waste and improvement opportunities.

Poka-Yoke

Error prevention techniques that make it impossible or immediately obvious when mistakes occur.

Gemba

Japanese term meaning "the real place" where value is created. Refers to going to the actual workplace to observe processes.

Waste Types

Muda

Japanese term for waste - any activity that consumes resources but creates no value for the customer.

Seven Wastes

Traditional categories of waste: Transportation, Inventory, Motion, Waiting, Overproduction, Over-processing, Defects.

Value-Added Activity

Any activity that transforms a product or service in a way the customer is willing to pay for.

Non-Value-Added Activity

Activities that consume resources but do not add value from the customer's perspective.

Professional training from Eastman Business Institute covers both Six Sigma and Lean methodologies in integrated programs.

Project Management and Implementation Terms

Project Elements

Project Charter

Document that formally authorizes a Six Sigma project and defines scope, objectives, and success criteria. Use our project charter template.

Voice of Customer (VOC)

Process of capturing customer requirements, expectations, and feedback to drive improvement priorities.

Critical to Quality (CTQ)

Characteristics that are most important to customer satisfaction and must be measured and controlled.

SIPOC

High-level process map showing Suppliers, Inputs, Process, Outputs, and Customers.

Control Plan

Document that outlines the monitoring and response procedures needed to sustain process improvements.

Measurement and Analysis

Baseline

Current performance level before improvement efforts begin, used as a reference point for measuring progress.

Key Performance Indicator (KPI)

Metrics used to evaluate the success of an organization or activity in meeting objectives.

Measurement System Analysis (MSA)

Statistical study to evaluate the adequacy of measurement systems, often using Gage R&R studies.

Gage R&R

Study that measures the amount of variation in a measurement system due to Repeatability and Reproducibility.