Active Directory
Active Directory (AD) is a directory service for Windows network environments. It is a distributed, hierarchical structure that allows for centralized management of an organization’s resources, including users, computers, groups, network devices, file shares, group policies, devices, and trusts. AD provides authentication and authorization functions within a Windows domain environment.
AD is essentially a sizeable read-only database accessible to all users within the domain, regardless of their privilege level. A basic AD user account with no added privileges can enumerate most objects within AD.
There is a mindmap for Active Directory -