There are at least three different meanings used with the term Six Sigma.

1. A philosophy or understanding that defects cost money. A way to become more profitable is to eliminate the defects. Organizations that do this have a lower cost structure and are more likely to have loyal customers.

2. Six Sigma is a performance metric. Meaning that the product or service is performing at a level where the chances of a defect are less than 3.4 in a million opportunities. The 3.4 ppm defect rate is for a not what you find if you look at a normal distribution table considering both tails. Six Sigma is about 2 ppb (parts per billion) one ppb on the high side and one ppb on the low side. In a later module we will explore why the 1.5 standard deviation shift of the mean produces no more than 3.4 ppm defective.

3. Six Sigma is a methodology for working on projects utilizing specific phases. These are Define, Measure, Analyze, Improve, and Control. When Six Sigma is used to describe a project, it is the application of these different steps for a specific project. The goal of the project is 3.4ppm defective or less.