The expression "5x3" represents a multiplication operation where the number 5 is multiplied by the number 3. This means you are adding the number 5 together three times: 5 + 5 + 5. The result of this operation is 15. In mathematical terms, multiplication is a way to find the total of equal groups. In this case, there are three groups of 5, leading to the same result of 15. This concept is fundamental in arithmetic and is used in various applications, from simple calculations to more complex mathematical problems.