The modulo operation, often represented as a mod b, calculates the remainder when one number, a, is divided by another number, b. For example, in the expression 7 mod 3, the result is 1 because when 7 is divided by 3, it goes 2 times with a remainder of 1. This operation is widely used in computer science, mathematics, and programming. It helps in tasks like determining even or odd numbers, cycling through arrays, and managing time calculations, such as finding the day of the week for a given date.