Process Variation Explained
At the heart of Six Sigma is the principle of Process Variation. Six Sigma assumes that everything is a result of some process, therefore, if your product quality varies then this is the result of variation in the process that creates that product. To understand Six Sigma means that you first have to accept that variation exists in everything. Sometimes the variation may be too small to detect but it is still there.
Sigma, the eighteenth letter of the greek alphabet is also the mathematical symbol for Standard Deviation, a measure of variation and defects in a business process or Process Efficiency.