Hi,

Polymorphic means the polymorphism i.e an object that has a IS-A relation with their own type class object. Hibernate query doesn't only returns the instance of parent class, it returns the instances of subclasses also i.e a query will return all those persistent classes instance which extends that class or an interface is implemented.

Fore detail on http://www.roseindia.net/hibernate/hibernate4/hibernatePolymorphicQueries.shtml