What is the meaning of Polymorphism?

The ability to assume different forms or shapes.

The coexistence, in the same locality, of two or more distinct forms independent of sex, not connected by intermediate gradations, but produced from common parents.

The feature pertaining to the dynamic treatment of data elements based on their type, allowing for an instance of a method to have several definitions.

The property of certain typed formal systems of allowing for the use of type variables and binders/quantifiers over those type variables; likewise, the property of certain expressions (within such typed formal systems) of making use of at least one such typed variable.

The ability of a solid material to exist in more than one form or crystal structure; pleomorphism.

The regular existence of two or more different genotypes within a given species or population; also, variability of amino acid sequences within a gene's protein.

Source: wiktionary.org