Let's see ... polymorphism is one of the main characteristics of the object
oriented programming paradigm along with inheritance and data encapsulation.
As others have explained polymorphism is the same form with different
shapes, as it pertains to Java, it is just the same name used in different
methods, as in overriding and overloading.

Check
java.sun.com/.../override.html
And
forum.java.sun.com/thread.jspa