Intro to Combinations and Permutations

Combination
A combination is a way of choosing items from a group, when the order does not matter. For example, if you want to take 2 fruits for your lunch and you have 3, you will need to choose 2 fruits from 3, but you probably don't care what order you take them in.

Permutation
Permutation is just a fancy word for "order", and it refers to an ordered combination. For example, let's say you're the judge of a poetry contest with different prizes for 1^st, 2^nd and 3^rd place. In this case, order matters, so you care both about choosing the winners and ordering them. In fact, sometimes you may order an entire set of elements without even choosing them, such as if you were ranking an entire class of poets. Both these cases are known as permutations.

Example
In a combination, you just care what was chosen, not what order it is in. So {Anna, Bill, Charlie} is the same combination as {Charlie, Anna, Bill}, but a different permutation.