In Active Directory, a directory partition is a portion of the directory namespace. Each directory partition contains a subtree of directory objects in the directory tree. The same directory partition can be stored as replicas on many domain controllers, and the copies are updated through directory replication.

An application directory partition is a directory partition that is replicated only to specific domain controllers. The domain controller that participates in the replication of a particular application directory partition hosts a replica of that partition.

Application directory partitions most often are used for storing dynamic data. They provide the ability to control the scope of replication and allow the placement of replicas to match the type of dynamic data stored on the partition. As a result, the application directory partition provides the capability of hosting dynamic data in the Active Directory Server, thus allowing ADSI/LDAP access it, without significantly impacting network performance.