an object name, an attribute and an operation (method).

Classes: A class is a collection of objects with the same properties and the same operations. Each class generally has instances; a class without instances is an abstract class. Inheritance: Inheritance is a mechanism by which different classes in a hierarchical association of a class share properties and operations. For two classes A and B, if class A is a subclass of class B, then class B is a generalisation of class A.