Six Sigma is a data-driven approach to process improvement that focuses on reducing variability in processes by identifying and eliminating defects. It involves applying statistical methods and tools to measure a process's performance, systematically analyze sources of defects and variability, and implement solutions. Six Sigma follows five phases known as DMAIC: Define, Measure, Analyze, Improve, and Control. The goal of Six Sigma is to reduce defects to 3.4 defects per million opportunities. Key principles of Six Sigma include having a customer focus, identifying root causes of problems, eliminating sources of variation, using a team-based approach, being flexible, and taking a thorough problem-solving approach.