There's an operator in programming that allows you to calculate the remainder when dividing two numbers. Its often denoted by a percent sign: %.
For example: 5 % 2 = 1, if you imagine there being bracketed slots that can hold 2 stars each, then it would look like this: [**] [**] [* ]. Since one of the brackets isn't filled completely, that means there's a remainder. In this case its one since that's the number of stars left over when you count the complete ones: [* ].
I tend to call it Modulus but its also referred to as the Modulo operation. Here's the wiki article if you wanna read more about it: