Fully qualified domain name

[2] A fully qualified domain name is distinguished by its lack of ambiguity in terms of DNS zone location in the hierarchy of DNS labels: it can be interpreted only in one way.

The top of the hierarchy in an FQDN begins with the rightmost label.

[3] The topmost layer of every domain name is the DNS root zone, which is expressed as an empty label and can be represented in an FQDN with a trailing dot, such as somehost.example.com.. A trailing dot is generally implied and often omitted by most applications.

Trailing dots are required by the standard format for DNS zone files, as well as to disambiguate cases where an FQDN does not contain any other label separators, such as the FQDNs for the root zone itself and any top-level domain.

Dot-separated domain names are not used in the internal representation of labels in a DNS message[7] but are used to reference domains in some TXT records and can appear in resolver configurations, system hosts files, and URLs.