Domain name is a 'word form' describing a numerical Internet Protocol (IP) address of an internet computer or system, which is owned by a registrant of that name. 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[1]
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 domain name would be "www.conservapedia.com".
Subdomain
The first portion of a domain name (usually "www") is known as a subdomain.
Top-level domain
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), and ".mil" (military institution). Other countries have their own TLDs, such as Britain's ".co.uk" and Germany's ".de" TLD.