Six Sigma is a data-driven methodology for eliminating defects in any process. It aims to achieve a goal of 3.4 defects per million opportunities. The key concepts of Six Sigma revolve around critical quality attributes, defects, process capability, and variation. There are two main methodologies - DMAIC for improving existing processes and DMADV for designing new processes. Both follow the five steps of Define, Measure, Analyze, Improve/Design, and Control/Verify. Implementing Six Sigma requires roles like Champions, Master Black Belts, Black Belts, and Green Belts.