The expression '5' * '3' evaluates to 15 (a number). Unlike the + operator which can perform string concatenation, the * operator always attempts to convert its operands to numbers. So, the strings '5' and '3' are converted to the numbers 5 and 3, and then 5 * 3 equals 15. This is an example of JavaScript's implicit type coercion, where strings that represent valid numbers are automatically converted to numbers in a numeric context.