A hostname is the unique Fully Qualified Domain Name (FQDN) that contains the domain and a computer name for the purposes of unique identification of each computer used in the internet. It can be one or a combination of labels that help identify a computer in the Domain Name System (DNS) hierarchy naming. To qualify as a FQDN however, the hostname should have specified labels up to the Top-Level Domain Name (TLD). In en.xyz.org, en is the host name; .xyz is the domain name and .org the TLD. The hostname makes connecting to the computer easier since the user is not required to type out the numeric address that may prove hard for a lot of users to master.
When using a hostname, the user types it fast before typing the domain name. The two are separated by a period (.). The hostname further allows the host to be identified easily in the diverse electronic communication forms like email, Usenet and World Wide Web. In simple terms, the hostname is a human readable computer identity, which corresponds to the unique electronic device thus giving it uniqueness and validity within the network of other computers. Hostnames are common use in the browser lists of computer connected to the internet, email headers and directory lists. They are also common in a local network setup in which case, they can be a single word or more. In the internet contest, a host name cannot be used without the domain name. The two are then translated to an internet protocol address through the host files or the DNS resolve.
However, it is not uncommon to see the domain name acting as the host name. For example in en.xyz.org, where en is the host name and xyz.org the domain name, xyz.org can double up as the host name as long as it has an IP address assigned to it. In the event where the domain name has not been assigned an IP address independent of the hostname, then it cannot be recognized as a hostname. Hostnames are made up of bales and dots, with each label having 1 to 63 characters. The entire hostname should not exceed 255 characters. The labels are made of letters from ‘a’ to ‘z’ and can be from either uppercase or lower case. Numbers can only be from zero to ’9′. In addition, a hyphen can be used but no other form of punctuation or spacing in between characters is allowed.