The expression "2!" represents the mathematical concept of factorial. The factorial of a number is the product of all positive integers from that number down to 1. For example, "2!" means you multiply 2 by 1, which equals 2. Factorials are commonly used in various areas of mathematics, including combinatorics and probability. They help calculate permutations and combinations, which are essential for determining the number of ways to arrange or select items. In this case, "2!" is a simple example, but factorials can grow rapidly with larger numbers.