Active Directory is a directory service for Windows 2000 Server. It stores information about various objects on the network and makes it easy for Administrators and Users to find and use. The Active Directory Service uses structured data storage as the basis of the logical hierarchy of directory information.
Security is integrated into Active Directory through login authentication and access control of objects in the directory. With a network login, the administrator can manage the directory data and units in the entire network, and authorized network users can access resources anywhere on the network. Policy-based management reduces the management of even the most complex network.
It is like a yellow page. You can tell the computer in detail that resources can be used in the computer network, making it easier for administrators to manage networks and users to use resources.