Daniel Hutmacher does the math:

The

modulusis the remainder of a division of two integers*. Suppose you divide 12 by 4, the result is 3. But divide 11 by 4, and the result is 2.75. This could also be expressed by saying that 11/4 is 2with a remainder of 3. Computing that 3 is the work of the modulo operator, which in T-SQL is represented by the % operator.Let’s explore how to compute the modulus of large numbers in SQL Server, and how this is useful in the real world.

Daniel’s example includes IBAN validation, though I think he’s secretly working on breaking asymmetric encryption…