Six Sigma is a methodology for process improvement that was originally developed by Motorola in the mid-1980s. The methodology uses data and statistical analysis to identify and eliminate defects in a process or product. The ultimate goal of Six Sigma is to achieve a level of quality that is near-perfect, with a defect rate of 3.4 defects per million opportunities.

The Six Sigma methodology is typically applied in a five-step process, known as DMAIC:

1. Define: Define the problem and the customer's requirements.
2. Measure: Measure the current process and collect data.
3. Analyze: Analyze the data to identify the root cause of defects.
4. Improve: Improve the process by eliminating the root cause of defects.
5. Control: Control the process to ensure that the improvements are sustained.

Six Sigma also emphasizes the importance of leadership and employee involvement in the process improvement effort, and it uses a range of tools and techniques to support this, including statistical process control, design of experiments, and lean principles.

Today, Six Sigma is widely used in a variety of industries, including manufacturing, healthcare, finance, and telecommunications, among others.