In general, a domain is an area of control or a sphere of knowledge.
1) In computing and telecommunication in general, a domain is a sphere of knowledge identified by a name. Typically, the knowledge is a collection of facts about some program entities or a number of network points or addresses.
2) On the Internet, a domain consists of a set of network addresses. This domain is organized in levels. The top level identifies geographic or purpose commonality .The second level identifies a unique place within the top level domain and is, in fact, equivalent to a unique address on the Internet IP ADDRESS. Lower levels of domain may also be used.
Strictly speaking, in the Internet's domain name system , a domain is a name with which name server records are associated that describe subdomains or host. For example, "yahoo.com" could be a domain with records for "www.yahoo.com" .
