The expression "4!" represents the mathematical operation known as factorial. The factorial of a number is the product of all positive integers from that number down to 1. For example, 4! means you multiply 4 by 3, then by 2, and finally by 1. So, 4! = 4 × 3 × 2 × 1. Calculating 4! gives you 24. Factorials are commonly used in various areas of mathematics, including combinatorics, which deals with counting and arranging objects. Understanding factorials is essential for solving problems related to permutations and combinations.