An FQDN, or Fully Qualified Domain Name, is written using the hostname and the domain name, including the top-level domain, in that order: [hostname].[domain].[tld].
Deconstructing a Fully Qualified Domain Name (FQDN)
In this scenario, "qualified" means "specified," since the full location of the domain is specified in the name. The FQDN specifies the exact location of a host within DNS. If the name is not so specified, it is called a partial qualified domain name, or PQDN. You can find more information about PQDNs at the bottom of this page.
An FQDN is also called an absolute domain name because it represents the absolute path of the host.
A fully qualified domain name is always written in this format: [hostname].[domain].[tld]. For example, a mail server at the domain example.com might use the FQDN mail.example.com.
