A metric that indicates how well a process is performing. The higher the sigma value, the higher the performance quality of the organization’s process. Sigma measures the capability of the process to perform defect-free work, with a defect being anything that results in customer dissatisfaction. Six sigma targets a defect rate or level of quality that only permits 3.4 errors (or variations) per million opportunities, 6 sigma. Six sigma typically strives for quantum leaps in improvement.