What Is A Polymorphism In Java?

Polymorphism is a feature in Java that allows us to create a variable in the superclass so that we can reference an object in the subclass. This way, we can make it possible to use the variable whose value we don't know until at a certain stage in the program. Normally, a value is assigned to this variable only when certain conditions are fulfilled, hence at runtime (late binding).
It is a feature of Object Oriented Programming that allows methods to do different things based on the objects they are acting upon.
Inheritance (using properties of one class while adding own functionality in another class) uses the keyword 'extends' and works together with polymorphism to achieve the desired results.
Hope this helps :-)

In Java like programming language, Polymorphism allows values of different data types to be handled using a uniform interface. Actually The concept of parametric polymorphism applies to both data types and functions.
So we can say: A function that can evaluate to or be applied to values of different types is known as a polymorphic function.