Greek Small Letter Sigma

Sigma (σ) represents the eighteenth letter of the Greek alphabet and is pronounced as a voiceless alveolar sibilant, similar to the English letter s. It belongs to the Greek and Coptic script block and serves as the lowercase counterpart to the capital letter Σ. Unlike its final form variant used at the ends of words, this medial version appears at the beginning or in the middle of Greek words.

Beyond its linguistic origins, this character is a standard mathematical symbol frequently found in scientific and technical documentation. It commonly denotes the standard deviation in statistics, representing the measure of variation within a data set. In the field of physics, it is used to signify Stefan-Boltzmann constants or surface charge density. Engineers and material scientists also utilize the symbol to represent normal stress in structural calculations.