There are three predefined Naming Contexts (NC)
1. Domain Naming Context
2. Configuration Naming Context
3. Schema Naming Context
1. Domain Naming Context - One per domain. The domain naming context stores users, computers, groups, and other objects for that domain. All domain controllers that are joined to the domain share a full writeable copy of the domain directory partition. Additionally, all domain controllers in the forest that host the global catalog also host a partial read-only copy of every other domain naming context in the forest.
2. Configuration Naming Context - One per forest. It stores forest-wide configuration data that is required for the proper functioning of Active Directory as a directory service. Information that Active Directory uses to construct the directory tree hierarchy is also stored in the configuration directory partition, as is network-wide, service-specific information that applications use to connect to instances of services in the forest. Every domain controller has one fully writeable copy of the configuration directory partition.
3. Schema Naming Context - One per forest. The schema naming context contains the definitions of all objects that can be instantiated in Active Directory. It also stores the definitions of all attributes that can be a part of objects in Active Directory. Every domain controller has one fully writeable copy of the schema directory partition, although schema updates are allowed only on the domain controller that is the schema operations master.
You can also define your own naming context in Windows 2003 and later -- called Application Partitions. Replication issues are not specific to a naming context.
