The notation "9!" represents the factorial of the number 9. Factorial is a mathematical operation that multiplies a whole number by all the positive whole numbers less than it. For example, 9! is calculated as 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1, which equals 362,880. Factorials are commonly used in various fields, including combinatorics, probability, and statistics. They help in calculating permutations and combinations, which are essential for determining the number of ways to arrange or select items from a set.