These are access specifiers for class data members and member methods.

1. Public:  The data members and methods having public as access specifier can be accessed by the class objects created outside the class.
2. Protected: The data members and methods declared as protected will be accessible to the class methods and the derived class methods only.
3. Private: These data members and methods will be accessible from the class methods only, not from derived classes and not from objects created outside the class.
4. Internal: Some languages define internal as an access specifier which means the data member or method is available to all the classes inside that particular assembly.
5. Friend: A friend class or method can access all data of a class including private and protected data.