WHAT IS the DOMAIN

The term domain name has multiple related meanings:

• A name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.
• The product that domain name registrars provide to their customers. These names are often called registered domain names.
• Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domain names like .com, or the names used by the Session Initiation Protocol (VoIP), or DomainKeys.
• They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".

This article will primarily discuss registered domain names. See the Domain Name System article for technical discussions about general domain names and the hostname article for further information about the most common type of domain name.

if you want to see all article here is the source
source : http://en.wikipedia.org/wiki/Domain_name