(general) The ability to assume different forms or shapes.
(biology) Polymorphism occurs when different phenotypes exist in the same population of a species. It is independent of sexual variations, and not connected by intermediate gradations but produced from common parents.
Word origin: From Ancient Greek poly (many) + morph (form) + -ism.
Related forms: polymorphic (adjective), polymorph (noun).
Related term: genetic polymorphism