The expression 5 × 4 × 3 × 2 × 1 represents the factorial of the number 5, denoted as 5!. Factorials are used in mathematics to calculate the total number of ways to arrange a set of items. In this case, 5! calculates the number of ways to arrange 5 distinct objects. To compute 5!, you multiply the numbers from 5 down to 1. This results in 5 × 4 = 20, then 20 × 3 = 60, followed by 60 × 2 = 120, and finally 120 × 1 = 120. Therefore, 5! equals 120, indicating there are 120 unique arrangements of 5 items.