Glossary

Lean Six Sigma glossary

The terms you actually run into, in plain English. Where a term has a free calculator, it links straight to it.

5 Whys

A root-cause technique: ask "why" repeatedly (often five times) until you reach the underlying cause of a problem rather than a symptom.

A3

A one-page structured problem-solving report, named for the paper size, that walks from background and current state to root cause, countermeasures, and follow-up.

Control Chart

A time-ordered plot of a process metric with statistical control limits, used to tell normal variation apart from a real change that needs action.

COPQ (Cost of Poor Quality)

The total cost a business carries because work is not done right the first time: scrap, rework, returns, and lost goodwill. COPQ calculator →

Cp

A process capability index comparing the spread of a process to the width of its specification. It assumes the process is centered. Cp / Cpk calculator →

Cpk

A capability index that accounts for how far off-center a process runs. Cpk is never higher than Cp, and a common target is 1.33 or above. Cp / Cpk calculator →

CTQ (Critical to Quality)

The measurable characteristics of a product or service that matter most to the customer, translated from broad needs into specific requirements.

DMAIC

The core improvement cycle: Define, Measure, Analyze, Improve, Control. It moves a team from a vague problem to a controlled, sustained fix. What is a process audit →

DPMO

Defects Per Million Opportunities. A volume-independent defect rate that lets you compare very different processes on the same scale. DPMO & sigma calculator →

FMEA

Failure Mode and Effects Analysis: a structured review of how a process can fail, how bad each failure is, and where to act first.

Gemba

Japanese for "the real place." In improvement work it means going to where the work actually happens to see the process first-hand.

Kaizen

Continuous improvement through many small, frequent changes made by the people who do the work, rather than rare large projects.

Kanban

A visual system that signals when to start work and limits how much is in progress at once, keeping flow smooth and bottlenecks visible.

Muda

Japanese for "waste." The activities in a process that consume time or resources without adding value the customer would pay for.

Pareto Principle

The observation that roughly 80 percent of effects come from 20 percent of causes, used to focus effort on the few problems that matter most.

PDCA

Plan, Do, Check, Act: a short iterative loop for testing a change on a small scale before adopting or adjusting it.

Poka-Yoke

Mistake-proofing: designing a step so the error simply cannot happen, or is caught immediately, instead of relying on people to be careful.

RPN (Risk Priority Number)

In an FMEA, the product of severity, occurrence, and detection scores. Higher numbers flag the failure modes to address first.

Sigma Level

A measure of process capability on the Six Sigma scale. Six sigma corresponds to about 3.4 defects per million opportunities. DPMO & sigma calculator →

SIPOC

A high-level map of a process: Suppliers, Inputs, Process, Outputs, Customers. It frames scope before deeper analysis begins.

Standard Work

The current best-known way to perform a task, documented and followed consistently so improvement has a stable baseline to build on.

Takt Time

The pace of customer demand: available work time divided by units required. It sets the rhythm a process must hold to keep up.

Value Stream Map

An end-to-end diagram of the steps, delays, and information flow that turn a request into a delivered outcome, used to expose waste.

VOC (Voice of the Customer)

The structured capture of what customers need and expect, used to define what good means before a process is measured or changed.