The capital Greek letter (capital sigma) is used in algebra to represent the summation operator. Typically, the symbol appears in an expression like this:
In plain language this expression means sum together the expressions represented by starting from and ending when .
The Greek letter σ (sigma) is used in statistics to represent the standard deviation of a population.
The summation operator is represented by the symbol Σ (capital sigma) and represents the operation of summing a sequence of expressions together. The operator is used in math to represent the sequence and series.