What is Active Directory Domain and Domain Controller?

The primary unit of logical structure in Active Directory is the Active Directory domain. Active Directory domain is also an Active Directory container which can hold a large number of other Active Directory objects like users, computers, printers, shared folders, groups etc.

Active Directory domain allow centralized management and control of Active Directory objects (Active Directory users, computers, printers, shared folders, groups etc). Every object within an Active Directory domain is controlled by the same security policies and access restrictions.

An Active Directory domain is the security boundary that controls authentication of users, access to resources available in the Active Directory, and trusts with other Active Directory domains.

First domain is implemented when Active Directory is installed on the first domain controller in that domain.

Following figure explains the relation between an Active Directory forest, Active Directory tree and an Active Directory domain.