Polymorphism is a property of OOP that allows an object to take on many forms. It enables a single interface to represent different underlying data types, so that the same function or method can operate on objects of different classes. Polymorphism promotes flexibility and reusability in code, allowing developers to write more general and extensible programs. It is typically achieved through method overriding and method overloading, and is a core concept in languages like Java, C++, and Python.