For example, in mozilla.org the SLD is mozilla and the TLD is org .

A domain name is not limited to a TLD and an SLD. Additional subdomains can be created in order to provide additional information about various functions of a server or to delimit areas under the same domain. For example, www is a commonly used subdomain to indicate the domain points to a web server.

As another example, in developer.mozilla.org , the developer subdomain is used to specify that the subdomain contains the developer section of the Mozilla website.