Six Sigma is a data-driven methodology for process improvement that focuses on reducing defects. It aims for near perfection by striving for no more than 3.4 defects per million opportunities. The document discusses the key principles and tools of Six Sigma including defining critical customer requirements, measuring processes and quality, analyzing data to identify sources of variation, improving processes by addressing key causes of defects, and controlling processes to sustain improvements. It also explains the DMAIC methodology for improving existing processes and DMADV for designing new processes.