Abstract class A class that has no objects.
Abstract method A method without an implementation; an abstract method is defined in an interface or abstract class.
Abstraction The process of forgetting information so that things that are different can be treated as if they are the same. Also, the program entity that results from the abstraction process.
Abstraction by parameterization The process of abstracting from the identity of specific data items by replacing them with parameters.
Abstraction by specification The process of abstracting from how a program module is implemented to what the module does.
Abstraction function A mapping from the rep of an object to the abstract state that the rep is intended to represent.