The FQDN (Fully Qualified Domain Name), say fully qualified domain name, or an absolute domain name, a domain name that specifies the exact location of the Domain Name System (DNS) tree hierarchy. It defines each domain level, including at least one second level domain and one top level domain. A fully qualified domain name is distinguished by a lack of ambiguity: it can only be interpreted in one way.

A fully qualified domain name consists of a list of domain name tags that represent a hierarchy from the lowest level of the DNS to the top level domain. The FQDN is divided into several parts by points, e.g. gepneve.pelda.hu., where the last dot indicates the root domain, but is not usually printed because DNS address resolutions are automatically appended to the name during processing. Unlike a fully qualified domain name, a domain name that does not include full path tags to the DNS root is often considered a partially qualified domain name.

Some applications, such as web browsers, try to interpret the domain name as a URL if the address resolver does not find the specified domain. However, other applications do not use a separator to indicate completeness because the protocols behind it require the use of FQDN (eg email).