What is a 'enum' ?

Answer 1

It's enumerated type, example of it in C++ would be like this.
enum class Color {Red, Green, Blue};

Using an enum allows you iterate trough a list of objects you defined.

Answer 2

Basically, Enums define variables that represent members of a fixed set.

Answer 3

An Enum is a special type used to define collections of constants.

Answer 4

enum is a constant