Combination : In combinatorics a combination is a selection of a subset from a set. There are $\binom{n}{k}$ different combinations that choose $k$ objects out of $n$ possible objects. For example if there is a league with 5 soccer teams, there are $\binom{5}{2}=\frac{5!}{3!2!}=10$ different possible match-ups. In chess a combination is a series of moves that results in a material or positional gain.