The Free On-line Dictionary of Computing (30 December 2018):

fully qualified domain name
domain name
FQDN

    (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.

   See also network, the, network address.

   (2005-06-09)