In object-oriented programming, polymorphism refers to a programming language's ability to process objects differently depending on their data type or class. Furthermore, it is the ability to redefine methods for derived classes. Example: Given a base class shape, polymorphism enables the programmer to define different area methods for any number of derived classes, such as circles, rectangles and triangles. No matter what shape an object is, applying the area method to it will return the correct results. Polymorphism is considered to be a requirement of any true object-oriented programming language (OOPL).