Active Directory Question:

The Active Directory schema is the set of definitions that defines the kinds of objects, and the
types of information about those objects, that can be stored in Active Directory. The
definitions are themselves stored as objects so that Active Directory can manage the schema
objects with the same object management operations used for managing the rest of the
objects in the directory.
There are two types of definitions in the schema: attributes and classes. Attributes and
classes are also referred to as schema objects or metadata.
Attributes are defined separately from classes. Each attribute is defined only once and can be
used in multiple classes. For example, the Description attribute is used in many classes, but is
defined once in the schema, assuring consistency.