Final answer:
An FQDN consists of a hostname, domain name, and a top-level domain (TLD) which uniquely identifies a device on the Internet.
Step-by-step explanation:
A fully qualified domain name (FQDN) must contain the hostname, domain name, and top-level domain (TLD). The FQDN uniquely identifies a device on the internet and establishes its position within the domain hierarchy. For example, in 'www.example.com', 'www' is the hostname, 'example' is the second-level domain, and '.com' is the TLD, which is the highest level of the domain structure on the internet.