What is sigma meaning?

Sigma (Σ) is the 18th letter of the Greek alphabet and is often used as a symbol in mathematics, science, and engineering. It represents the sum of a series or sequence of numbers or values. In statistics, the term "standard deviation" is denoted by the Greek letter sigma, which is used to measure how much a set of data varies from its mean. Sigma is also used as a symbol in chemistry to denote a bond angle, and in physics to represent the stress tensor. In business, the term "Six Sigma" refers to a methodology for improving processes and reducing defects, with the name derived from the statistical definition of sigma.