A contiguous subtree of Active Directory that is replicated as a unit to other domain controllers in the forest that contain a replica of the same subtree. In Active Directory, a single domain controller always holds at least three directory partitions: schema (class and attribute definitions for the directory), configuration (replication topology and related metadata), and domain (subtree that contains the perdomain objects for one domain). Domain controllers running Windows Server 2003 can also store one or more application directory partitions.