Six Sigma is a set of techniques and tools for process improvement that aims to reduce defects to 3.4 per million opportunities. It was introduced by Motorola in 1986 and uses methodologies like DMAIC for improving existing processes and DMADV for creating new processes and designs. The Mumbai Dabbawalas apply Six Sigma principles through techniques like just-in-time delivery, teamwork, discipline, and honesty to achieve an extremely low error rate of 1 in 16 million deliveries.