Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. It serves as a centralized repository for network resources, allowing administrators to manage and organize users, computers, groups, and other network objects. Active Directory provides a variety of services, including:

Authentication: Active Directory authenticates and validates the identity of users and computers logging into the network. It supports various authentication protocols such as Kerberos and NTLM.

Authorization: Once authenticated, users and computers are granted access to network resources based on their assigned permissions and security policies defined within Active Directory.

Directory Services: Active Directory stores information about network objects in a hierarchical, tree-like structure known as the Active Directory Domain Services (AD DS). This structure organizes objects such as users, groups, computers, and organizational units (OUs) into logical containers called domains.