Six Sigma has three basic parts, which are process improvement, process design/redesign, process management. These parts are important because these three parts affect your organization and the process that were established and are in use on a daily basis. Six Sigma teams when the project is focused on process improvement finds the critical Xs (causes) that create the unwanted Ys (defects) produced by the process.

p. 13-14 - The six sigma way, 2000