forest functionality

forest functionality: The functional level of an Active Directory forest that has one or more domain controllers running Windows Server 2003. The functional level of a forest can be raised to enable new Active Directory features that will apply to every domain in the forest. There are three forest functional levels: Windows 2000, Windows Server 2003 interim, and Windows Server 2003. The default forest functional level is Windows 2000. When the forest functional level is raised to Windows Server 2003 interim or Windows Server 2003, advanced forest-wide Active Directory features are available.