The latin letter a is used to represent a variable or coefficient.
A variable is a core concept in algebra where a symbol, usualy a lower case latin letter, is used as a placeholder in a math expression.
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 capital Latin letter A is used in mathematics as a variable. In linear algebra the symbol is used to represent a matrix. In probability the symbol is used to represent a random variable. The symbol also appears in various formulas.