Plural Noun: domains;
IN COMPUTING :
A distinct subset of the Internet with addresses sharing a common suffix or under the control of a particular organization or individual.
A domain name locates an organization or other entity on the Internet. For example, the domain name “www.google.com” locates an Internet address for “google.com” at Internet point 220.127.116.11 and a particular host server named “www.” The “.com” part of the domain name reflects the purpose of the organization or entity (in this example .com means “commercial”) & is called the top-level domain name. The “google” part of the domain name defines the organization or entity & together with the top-level is called the second-level domain name. The second-level domain name maps to & can be thought of as the “readable” version of the Internet address.
A third level can be defined to identify a particular host server at the Internet address. In our example, “www” is the name of the server that handles Internet requests. (A second server might be called “www2.”) A third level of domain name is not required. For example, the fully-qualified domain name could have been “google.com” & the server assumed.
Subdomain levels can be used. For example, you could have “www.example.google.com.” Together, “www.google.com” constitutes a fully-qualified domain name.
Second-level domain names must be unique on the Internet & registered with one of the ICANN-accredited registrars for the .COM, .NET & .ORG top-level domains. Where appropriate, a top-level domain name can be geographic. (Currently, most non-US domain names use a top-level domain name based on the country & the server is in.) To register a US geographic domain name or a domain name under a country code, see an appropriate registrar.
On the Web, the domain name is that part of the Uniform Resource Locator(URL) that tells a domain name server using the domain name system (DNS) whether & where to forward a request for a Web page. The domain name is mapped to an IP address (which represents a physical point on the Internet).
More than one domain name can be mapped to the same Internet address. This allows multiple individuals, businesses & organizations to have separate Internet identities while sharing the same Internet server.
To see the IP address for a domain name, (Ping).
It may be worth noting that the domain name system contains an even higher level of domain than the top-level domain. The highest level is the root domain, which would be represented by a single dot (just as in many hierarchical file systems, a root directory is represented by a “/” ) if it were ever used. If the dot for the root domain were shown in the URL, it would be to the right of the top-level domain name. However, the dot is assumed to be there, but never shown.