This operation is a modulo operation, that is, it returns the remainder of the integer division of the first operand by the second. For example, 12 mod 5 would return 2, since 12 divided by 5 is 2 with remainder 2.

number mod number      // Returns number
currency mod number    // Returns currency
currency mod currency  // Returns number

Depends on operand value types

3 mod 1       // Returns 0
03 mod 2      // Returns 1
185 mod 43    // Returns 13
$42 mod $15   // Returns $12