Fully Quailified Domain Name

A fully qualified domain name (or FQDN) is an unambiguous domain name that specifies the node's position in the DNS tree hierarchy absolutely. To distinguish an FQDN from a regular domain name, a trailing period is added. ex: somehost.example.com. An FQDN differs from a regular domain name by its absoluteness; a suffix will not be added.

For example, given a device with a hostname of "myhost" and a domain name of "example.com", the fully qualified domain name is "myhost.example.com.". It therefore uniquely defines the device — whilst there might be many hosts in the world called "myhost", there can only be one "myhost.example.com.".

Notice that there is a dot at the very end of the domain name, i.e. it ends ".com." and not ".com" — this indicates that the name is an FQDN. For example "myhost.bar.com" could be ambiguous, because it could be the prefix of a longer domain name such as "myhost.bar.com.gov", whereas "myhost.bar.com." is a fully qualified domain name.