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 per-domain objects for one domain). Domain controllers running Windows Server 2003 can also store one or more application directory partitions.