Fully-Qualified Domain Name: A Domain Name that includes the labels of all superior nodes in the Internet

Domain Name System.

Informational Note: The term "fully qualified domain name" is not

well defined. In [RFC1034], it is also called an absolute domain

name, and the two terms are associated in [RFC1535]. The earliest

use of the term can be found in [RFC1123]. References to those

older specifications ought not to be construed as limiting the

characters of a fully qualified domain name to the ASCII range;

for example, [RFC5890] mentions that a fully qualified domain name

can contain one or more U-labels.

Fully qualified domain name (FQDN): This is often just a clear way

of saying the same thing as "domain name of a node", as outlined

above. However, the term is ambiguous. Strictly speaking, a

fully qualified domain name would include every label, including

the final, zero-length label of the root: such a name would be

written "www.example.net." (note the terminating dot). But

because every name eventually shares the common root, names are

often written relative to the root (such as "www.example.net") and

are still called "fully qualified". This term first appeared in

[RFC819]. In this document, names are often written relative to

the root.

The need for the term "fully qualified domain name" comes from the

existence of partially qualified domain names, which are names

where some of the right-most names are left off and are understood

only by context.