A fully qualified domain name (FQDN), sometimes also referred to as an absolute domain name. It is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It specifies all domain levels, including the top-level domain and the root zone. A fully qualified domain name is distinguished by its lack of ambiguity: it can be interpreted only in one way.
For example, www.example.com is an FQDN. www is the host; the area is the tertiary sector; example is the second level domain and .com is the top field.