Definition:Combination with Repetition

Definition
Let $S$ be a (finite) set with $n$ elements.

A $k$ combination of $S$ with repetition is a multiset with $k$ elements selected from $S$.

Also known as
Some sources give this as combination with repetitions, but the philosophical position of is that the singular form repetition is more grammatically flexible, in that it allows for a singular repetition, or indeed, no repetition at all.

Also see

 * Definition:Combination