The expression "7 % 3" represents the modulus operation, which finds the remainder when one number is divided by another. In this case, when you divide 7 by 3, the quotient is 2 because 3 goes into 7 two times, making 6. The remainder, which is what the modulus operation calculates, is 1. Thus, "7 % 3" equals 1. This means that if you take 7 and divide it by 3, you will have 1 left over. The modulus operation is commonly used in programming and mathematics to determine remainders in various calculations.