polymorph just means "many form(s)".
The definition in plain English

http://www.bartleby.com/61/66/P0426600.html

and narrower definitions in the context of computer programming

http://en.wikipedia.org/wiki/Polymorphism
http://wombat.doc.ic.ac.uk/foldoc/fo...&action=Search

don't really help us understand what polymorphism means
in the context...