A Dictionary is an unordered collection of mappings/associations from keys to values. It is very similar to a Set and has the same performance, but stores a key/value pair, and only the key has to be Hashable. It can be used for storing preferences, or when you have a group of named values that are either too many or change too often to be hardcoded. Then, you can use the names as keys.

The full name is Dictionary<Key, Value>, but it is more commonly written as [Key: Value].

Dictionary ignores the order in which values are added or removed, and may change it arbitrarily, just like Set.