A hostname is a label assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet. For example, "www" is a hostname for a web server.
A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). For instance, "example.com" is a domain name.
A Fully Qualified Domain Name (FQDN), sometimes also referred to as an absolute domain name, 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. An example of an FQDN is "www.example.com".
In the context of cloud services, for instance, when you want to deploy a website on a cloud server, you would need to specify the FQDN to ensure that users can access your website correctly. Tencent Cloud provides DNS services that can help manage your domain names and FQDNs efficiently.