What is what does sigma mean?

Sigma is a Greek letter used in statistics to represent standard deviation or the spread of a distribution of data. It is a measure of how much a set of data deviates from the average or mean value. A low sigma indicates that the data points are close to the mean, while a high sigma indicates that the data points are more spread out. Sigma is also used in Six Sigma methodology, which is a business management strategy used to improve processes and reduce defects. In this context, sigma refers to the number of standard deviations between the process mean and the nearest specification limit.