What is Factorial?

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. For example, 5! = 5 * 4 * 3 * 2 * 1 = 120. Factorials are commonly used in combinatorics, probability, and calculus, particularly in calculating permutations and combinations, and in Taylor series expansions.