As defined by Microsoft, in Active Directory server roles, computers that function as servers within a domain can have one of two roles: member server or domain controller. Abbreviated as DC, domain controller is a server on a Microsoft Windows or Windows NT network that is responsible for allowing host access to Windows domain resources. The domain controllers in your network are the centerpiece of your Active Directory directory service. It stores user account information, authenticates users and enforces security policy for a Windows domain.
See Active Directory.
See also member server.