The symbol "σ" (sigma) represents the mathematical operation of summation, which is used to add a series of numbers together. It is commonly used in statistics, mathematics, and various fields of science to calculate totals, averages, and other important values. The summation is typically expressed as Σ followed by an expression that defines the terms to be added, along with limits indicating the starting and ending points of the summation. In a summation, the index variable, often denoted as i, indicates the position of each term in the series. For example, Σ from i=1 to n of a_i means to sum the values of a_i for each integer i from 1 to n. This concise notation simplifies the representation of long sums and is essential for efficient calculations in various mathematical applications.