Class 

Definition

A class is a group of similar objects that have common characteristics. Classes allow you to group objects together according to criteria that you define.

Use

You create classes for objects, for example, for a casing. You use the class type to determine which object types can be grouped together in a class. You can assign characteristics to the class. These describe the objects that you classify in your class. If you assign a characteristic to a class, you can edit the characteristic further, at a later time.