FQDN

A fully qualified domain name (FQDN)is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It consists of a host and domain name, including top-level domain. 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 one way.

 host.domain.com

1. host = the first part of the FQDN is the hostname which can be www as an example. This is sometimes an alias called a cname.
2. domain = domain name hierarchy word
3. com = This is the TLD or top-level domain. Common examples are the original .com .net and .org.