DNS/RFC/8499について、ここに記述してください。

https://tools.ietf.org/html/rfc8499

DNS Terminology 

      Note that this is a definition independent of the DNS RFCs
      ([RFC1034] and [RFC1035]), and the definition here also applies to systems other than the DNS. 

      [RFC1034] defines the "domain name space" using mathematical trees and their nodes in graph theory,
      and that definition has the same practical result as the definition here.  

      Any path of a directed acyclic graph can be
      represented by a domain name consisting of the labels of its
      nodes, ordered by decreasing distance from the root(s) (which is
      the normal convention within the DNS, including this document).

      A domain name whose last label identifies a root of the graph is
      fully qualified; other domain names whose labels form a strict
      prefix of a fully-qualified domain name are relative to its first
      omitted node.

      Also note that different IETF and non-IETF documents have used the
      term "domain name" in many different ways.  It is common for
      earlier documents to use "domain name" to mean "names that match
      the syntax in [RFC1035]", but possibly with additional rules such
      as "and are, or will be, resolvable in the global DNS" or "but
      only using the presentation format".