Each Internet domain has a domain name to identify it. A domain name is a string of characters that can be translated into an IP address by computer systems connected to the Internet, using the DNS service.
In an internet address, the “www” part is the prefix (also called subdomain). Everything that follows is called the Root Domain. For example, mg.n0c.com, google.com and canada.ca are root domains. In the following example, the root domain is therefore “abc.xyz.ca“: www.abc.xyz.ca
See also label (of a domain name).