Six Sigma is a globally recognized brand for the concept aimed at reducing errors, through the use of structured processes. Six Sigma is based on statistical measurements - namely the standard deviation.
Six Sigma aims to reduce the DPMO (defects per million opportunities).
Six Sigmas methodolgy is based on DMAIC (Define, Measure, Analyze, Improve, Control). Six sigma has a range of qualifications that are represented as different "belts". Green Belt and Black Belt are the most commonly known qualifications.