Meaning

• A unique, case-insensitive, name, consisting of a string made up of alphanumeric characters and dashes separated by periods, that the Domain Name System maps to IP numbers and other information.

  "RFC 822, P. Mockapetris, November 1983: This RFC introduces domain style names, their use for ARPA Internet mail and host address support, and the protocols and servers used to implement domain name facilities."

• An identifier of a computer or site on the Internet

• A domain; that part of a domain name which (nominally) identifies an organization; a domain name delegated to an independent administrative authority who is then responsible for the management of that portion of the Domain Name System's namespace that consist of the delegated domain and all subdomains that are not delegated in turn.