Six Sigma is a set of methodologies and tools used to improve business processes by reducing defects and errors, minimizing variation, and increasing quality and efficiency. The goal of Six Sigma is to achieve a level of quality that is nearly perfect, with only 3.4 defects per million opportunities.

Six Sigma provides a systematic, data-driven framework for improving quality and empowering employees in these and many other industries. That framework rests on Six Sigma's five core principles: define, measure, analyze, improve, and control.

It's called Six Sigma because the term sigma refers to one standard deviation in a data set. The idea is that six such deviations should occur before the process results in a defect. When a process achieves Six Sigma, it reaches a point where only 3.4 errors per one million process events result in a defect.

Six Sigma. A business improvement approach that seeks to find and eliminate cause of defects and errors, reduce cycle times and cost of operations, improve productivity, better meet customer expectations, and achieve higher asset utilization.