A class which will not be used to instantiate objects.

"Hiding" properties and methods of a class from the "outside world" by making these private.

Implementing a method multiple times to accept different parameters.

Implementing an inherited method differently in a sub-class.

When a method or property can be accessed from outside the class.

When a method or property can only be accessed from inside the class.

A public method used to retrieve the content of a private property.

A public method used to set/overwrite the content of a private property.