The expression "4 × 5" represents a multiplication problem where the number 4 is multiplied by the number 5. In this case, 4 indicates that there are four groups, and each group contains 5 items. When you calculate "4 × 5," you find the total number of items in all groups combined. The result is 20, meaning there are twenty items altogether when you have four groups of five. This concept is fundamental in mathematics and is often used in various real-life situations, such as counting objects or organizing items.