The expression "5x4" represents a multiplication operation where the number 5 is multiplied by the number 4. This means you are adding the number 5 together four times: 5 + 5 + 5 + 5. The result of this operation is 20. In mathematical terms, "5x4" can also be written as 5 * 4, which is a common way to denote multiplication. This operation is fundamental in arithmetic and is often used in various applications, such as calculating areas or determining quantities in everyday situations.