Key Lean Six Sigma Green Belt terms in plain English. Understanding what each tool does - and which DMAIC phase it belongs to - is exactly what the exam tests.
| Term | Definition |
|---|---|
| Six Sigma | A data-driven methodology for reducing defects and variation in a process to improve quality. |
| Lean | An approach focused on maximising value and eliminating waste in a process. |
| DMAIC | The core improvement method: Define, Measure, Analyze, Improve, Control. |
| Define | The first DMAIC phase: framing the problem, scope, customer needs and project charter. |
| Measure | The DMAIC phase that maps the process and quantifies current performance with data. |
| Analyze | The DMAIC phase that identifies root causes using statistical tools. |
| Improve | The DMAIC phase that develops, pilots and implements solutions to the root causes. |
| Control | The DMAIC phase that sustains improvements with control plans and monitoring. |
| Project charter | A document that defines a project’s problem, scope, goals, team and timeline. |
| Voice of the Customer (VoC) | The expressed needs and expectations of the customer that drive requirements. |
| Critical to Quality (CTQ) | The specific, measurable customer requirements a process or product must meet. |
| SIPOC | A high-level process map of Suppliers, Inputs, Process, Outputs and Customers. |
| Process map | A diagram of the steps in a process, used to understand and improve flow. |
| Defect | Any output that fails to meet a customer requirement (a CTQ). |
| DPMO | Defects Per Million Opportunities: a standardised measure of defect rate. |
| Process capability (Cp, Cpk) | Indices that compare how well a process meets its specification limits. |
| Measurement System Analysis (MSA) | A check that the way data is measured is accurate and consistent. |
| Variation | The natural or special-cause spread in process outputs that Six Sigma works to reduce. |
| Hypothesis test | A statistical test used to decide whether a difference or effect is real or due to chance. |
| Correlation | A measure of how strongly two variables move together. |
| Regression | A statistical method that models the relationship between variables. |
| Fishbone diagram | A cause-and-effect (Ishikawa) diagram for brainstorming root causes. |
| Pareto chart | A bar chart ordering causes by frequency to find the vital few. |
| FMEA | Failure Mode and Effects Analysis: a method to anticipate and prioritise risks. |
| Poka-yoke | Mistake-proofing: designing a process so errors are hard or impossible to make. |
| Statistical Process Control (SPC) | Using control charts to monitor a process and detect unusual variation over time. |
| Kaizen | A philosophy and practice of continuous, incremental improvement. |