The Greek letter (sigma) is used in statistics to represent the standard deviation of a population.
Symbol  Format  Data 

σ  Unicode 

TeX 


SVG 
The standard deviation formula is denoted by the greek lower case sigma symbol in the case of the population and the latin letter s for the sample.
The Greek Alphabet is used throughout math to represent variables, constants, and coeffecients within math expressions, formulas, and equations.
The capital Greek letter Σ (Sigma) is used in algebra to represent the summation operator.