<networking> (FQDN) The full name of a system, consisting of its local hostname and its domain name, including a top-level domain (tld). For example, "venera" is a hostname and "venera.isi.edu" is an FQDN. An FQDN should be sufficient to determine a unique Internet address for any host on the Internet. This process, called "name resolution", uses the Domain Name System (DNS).
With the explosion of interest in the Internet following the advent of the web, domain names (especially the most significant two components, e.g. "sun.com", and especially in the ".com" tld) have become a valuable part of many companies' "brand". The allocation of these, overseen by ICANN, has therefore become highly political and is performed by a number of different registrars. There are different registries for the different tlds.
A final dot on the end of a FQDN can be used to tell the DNS that the name is fully qualified and so needs no extra suffixes added, but it is not required.