The capital Latin letter S is used in math to represent the partial sum of a series.
A series is the operation of adding an infinite number expressions together. A series is denoted using the summation operator and the index variable k.
The Latin Alphabet is a collection of 26 symbols that form the basis of the English language. The alphabet's symbols are used throughout mathematics to represent variables, constants, and coeffecients.
The latin letter s is used in statistics to represent the sample standard deviation.