Local subnetwork domains
On a local area network (LAN), a domain is a subnetwork made up of a group of clients and servers under the control of one central security database. Within a domain, users authenticate once to a centralized server known as a domain controller, rather than repeatedly authenticating to individual servers and services. Within a domain, individual servers and services accept the user based on the approval of the domain controller.
On the Internet, a domain is part of every network address. All devices sharing a common part of an address, or URL, are said to be in the same domain. In the address www.sahoster.com/people/address.shtml, sahoster is the domain, people is a directory in that domain, and address.shtml is a file in the directory.
To obtain a domain, you must purchase it from a domain registrar. You can choose a registrar from the list of accredited registrars.
Internet domains are organized by level. Most people are familiar with the Top Level Domains (TLDs) of .com, .edu, .net, and .org. TLDs are the most general and basic part of the URL. There are actually many top level domains. Every country is assigned one; see the complete list of country code Top Level Domains (ccTLDs).
Category domains called generic TLDs (gTLDs) are also available. These domains are described on the Internet Assigned Numbers Authority gTLD page.
The governing body for domain names is called ICANN (Internet Corporation For Assigned Names and Numbers), a non-profit corporation charged with overseeing the creation and distribution of TLDs.