Source : Free On-Line Dictionary of Computing

class hierarchy
     
         A set of {classes} and their interrelationships.
     
        One class may be a specialisation (a "{subclass}" or "{derived
        class}") of another which is one of its "{superclasses}" or
        "{base classes}".
     
        When a {method} is invoked on an {object} it is first looked
        for in the object's class, then the superclass of that class,
        and so on up the hierarchy until it is found.  Thus a class
        need only define those methods which are specific to it, and
        inherits methods from all its superclasses.
     
        See also: {multiple inheritance}.
     
        (1997-08-06)