A domain name locates an organization or other entity on the Internet.
For example, the domain name:
www.exabytes.com
Places the Internet address for "Exabytes.com" at IP Address 199.0.0.2 and a specific host server named "www". The word "com" is the part of the domain name that reflects the purpose of the organization or entity (in this example, "commercial") and is called the Top-Level-Domain (TLD). The word "exabytes" is the part of the domain name that defines the organization or entity and is referred to as the Second-Level-Domain. The Second Level Domain is commonly referred to as the version that can be read by Internet Addresses.
The third level can be defined to identify a specific host server on the Internet. For example "www" is the name of a server that handles Internet requests. (A second server is called "www2".)
The Sub Level Domain level can be used. For example, you could have "www.server.exabytes.com".
Thus, "www.exabytes.com" is a fully qualified domain name.
Second-Domain names must be unique on the Internet and registered with one of the ICANN-accredited Registrars for COM, NET, and ORG top-level domains.
On the Internet, a domain name is part of a Uniform Resource Locater (URL) that describes the name of a domain server using Domain Name Server (DNS). Domain name to place IP Address (represents physical on the Internet)
More than one domain name can be assigned to the same Internet Address. This is so that
