class hierarchy

organized structure of all classes and subordinate sub-classes (in object-oriented programming)

As in taxonomy, the classifications of species, a class hierarchy in computer science is a classification of object types, denoting objects as the instantiations of classes (class is like a blueprint, the object is what is built from that blueprint) inter-relating the various classes by relationships such as "inherits", "extends", "is an abstraction of", "an interface definition".
See more at Wikipedia.org...

<programming> 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)