The Greek letter s (sigma) refers to the standard deviation of a population. Sigma, or standard deviation, is used as a scaling factor to convert upper and lower specification limits to Z. Therefore, a process with three standard deviations between its mean and a spec limit would have a Z value of 3 and commonly would be referred to as a 3 sigma process.
The fundamental objective of the Six Sigma methodology is the implementation of a measurement-based strategy that focuses on process improvement and variation reduction through the application of Six Sigma improvement projects.
A charter is a document that establishes a purpose and plan for the project. It contains a statement of the problem, the scope of the project (including the process to be improved), an improvement goal, a plan and schedule for the project, estimated financial benefits, and a list of team members and their roles.