Domain name is a 'word form' entry in the Internet Domain Name System which is owned by a registrant of that name. Several kinds of entries can be associated with a domain name, including entries for routing email and entries for other kinds of interaction.
A fully qualified domain name (FQDN) is resolvable to a numerical Internet Protocol (IP) address of an internet computer or system. In layman's terms, it is analogous to the names in a telephone directory which are associated with a telephone number. The domain name is 'pointed to' the actual IP address of a given computer or network, and allows a user to remember how to access that service more easily than having to remember a complex string of numbers
Web servers, as is the case with all computers, are given IP addresses when on the Internet. IP addresses may be represented by domain names (this is called "name resolution"). One example of a fully-qualified domain name would be "www.conservapedia.com".
The first portion of a domain name (often "www") is known as a subdomain.
The last portion of a Web site's name is known as a top-level domain (or TLD). Common TLDs of US Web sites include ".com" (commercial site), ".org" (non-profit organization), ".edu" (educational institution), ".gov" (government institution), ".us" (any United States user) and ".mil" (military institution). Other countries have their own TLDs, such as Britain's ".co.uk" and Germany's ".de" TLD. The ".com" TLD is used by companies worldwide. Some country TLDs, such as ".tv" (Tuvalu) and ".fm" (Federated Micronesia), are resold outside their country because of their resemblance to common English terms. These country TLDs are based on the ISO 3166 standard country codes.
- Techtarget.com - Definition of Domain name