Firewall.cx, Microsoft.com, Idahojack.com, Symantec.com, etc. are all TLD’s (Top Level Domain’s), this would be called and treated as a website. WWW, FTP, WWW1, News, etc, are all “Sub-Domains”, they can be total different then the TLD’s.
Just because you have a TLD don’t really mean you have a sub-domain.
“WWW” are pointed to your TLD’s; you can have anything for a sub-domain.
And just because the whole world uses port 80 to serve a webpage that again does not really mean you have too, you could have a webpage on any 65535 ports you’d like.
However the first 1024 ports are reserved, but you could do it. The webpage Firewall.cx on port 80 may deal with firewalls but the Firewall.cx on port 2255 may deal with pretty flowers (there’s no page there, just for demo purposes).
Hope that helps muddy up the water more…I was in a hurry when I typed this up…
Jack is right, I just want to note that typically firewall.cx, microsoft.com, etc are Second Level Domains, TLDs are simply com, net, org, etc since they exist on the first level just under the root (.)
But of course we can consider a domain Top Level in accordance to our administration, that is if it is the highest Level Domain in our authority.