A network domain is an administrative grouping of multiple private computer networks or local hosts within the same infrastructure.[1][2][3] Domains can be identified using a domain name; domains which need to be accessible from the public Internet can be assigned a globally unique name within the Domain Name System (DNS).
A domain controller is a server that automates the logins, user groups, and architecture of a domain, rather than manually coding this information on each host in the domain. It is common practice, but not required, to have the domain controller act as a DNS server.[4] That is, it would assign names to hosts in the network based on their IP addresses.
A network domain is more formally defined as a group for servers controlled by a primary domain controller. The idea is that this group of servers can behave as a single combined unit.
The terminology, network domain, comes from the cellular systems. Traditionally, a cellular service provider owns not only radio frequency spectrums but also certain network infrastructure, for example, base stations, switches, and servers. All these entities are connected through wired network to provide telephony service. A network domain is the wired portion of an operator's network.