Schema Partition:

Only one schema partition exists per forest. The schema partition is stored on all domain controllers in a forest. It contains definitions of all objects and attributes that can be created in the directory.

Configuration Partition:

There is only one configuration partition per forest. the configuration partition contains information about the forest-wide active directory structure.

Domain Partition:

Many domain partitions can exist per forest. Domain partitions are stored on each domain controller in a given domain. A domain partition contains information about users, groups, computers, and organizational units.

Application Partition:

It stores information about applications in Active Directory. It is replicated only to specific domain controllers.