Third Level Domain Name
A domain name consists of three levels. The first level is the word or phrase that makes up the initial domain name. The second part of the domain name is the extension. Examples of common extensions include .com, .net or .org. The third portion of the domain name, called a third level domain name is an ... their setup. However, if they are used it's best that they are hidden in hyperlinks, since most website visitors would prefer to type in first level domain names.