A collection of things, in which the order does not matter.

Example: You are making a sandwich. How many different combinations of 2 ingredients can you make with cheese, mayo and ham?

Answer: {cheese, mayo}, {cheese, ham} or {mayo, ham}

When the order

Example: You are making a sandwich. How many different combinations of 2 ingredients can you make with cheese, mayo and ham?

Answer: {cheese, mayo}, {cheese, ham} or {mayo, ham}

When the order

**does**matter, such as a secret code, it is a PermutationSee: Permutation