High Quality Content by WIKIPEDIA articles! A Windows domain is a collection of security principals that share a central directory database. This central database (known as Active Directory starting with Windows 2000, Active Directory Domain Services in Windows Server 2008 and Server 2008 R2, also referred to as NT Directory Services on Windows NT operating systems, or NTDS) contains the user accounts and security information for the resources in that domain. Each person who uses computers within a domain receives his or her own unique account, or user name. This account can then be assigned access to resources within the domain.