An enum, or enumeration, is a user-defined data type in C++ that consists of named values representing integral constants. It provides a way to define and group integral constants, making the code easy to maintain and less complex. Enums are generally used when you expect the variable to select one value from the possible set of values, increasing the abstraction and enabling you to focus more on values rather than worrying about how to store them.

To define an enum, the keyword "enum" is used, followed by the name of the enum and the values assigned to the enumeration. For example, the following code defines an enum named "ice_cream_flavors" with five possible values:

enum ice_cream_flavors {
   vanilla,
   chocolate,
   strawberry,
   mint,
   caramel
};

Each of these elements has values starting from 0, like vanilla is 0, chocolate is 1, etc. . The default values mentioned can be altered during the declaration of the enum in C++ . Enums can also be used with switch statements.

Enums are helpful for code documentation and readability purposes. They can be used to create a new data type that has a fixed range of possible values, and the variable can select one value from the set of values.

In summary, an enum in C++ is a user-defined data type consisting of named values representing integral constants. It provides a way to define and group integral constants, making the code easy to maintain and less complex. Enums are generally used when you expect the variable to select one value from the possible set of values, increasing the abstraction and enabling you to focus more on values rather than worrying about how to store them.