Variation is the enemy of predictable quality. Six Sigma is a data-driven methodology for reducing defects and process variation so that outputs consistently meet customer requirements.

It uses a structured improvement cycle—Define, Measure, Analyze, Improve, Control—and statistical tools to find and remove root causes. Belts of varying expertise lead projects; sponsorship ensures results stick. The name refers to a defect rate of fewer than 3.4 defects per million opportunities.

Six Sigma works best on stable processes with measurable outputs. Combined with lean principles it addresses both waste and variation. Organizations that treat it as a rigid religion miss its practical core: disciplined problem solving backed by data.

• Methodology for reducing defects and variation
• Uses DMAIC and statistical analysis
• Aims for near-defect-free process performance
• Most effective with measurable, stable processes