Hostname

The hostname is a freely selectable name for a computer. For example, the server responsible for e-mail in a company can be given the host name “mailABC”.

If the computer is to be available not only locally, but also on the Internet, additional information must be added to the host name to form a name string, called a “Fully Qualified Domain Name” (FQDN). 

For example, in “mailABC.domainname.com”, “.com” is the TLD, “domainname” is the second level domain and “mailABC” would be the host name.