How do controllers on some websites come before the domain name followed by a dot?

I'm new to ASP.NET MVC, and I am just wondering how it's done with websites where you have as the URL what I think is the controller "." the domain name. Is that just some made up routing syntax?

Examples http://store.hp.com and http://ift.tt/1Ssm9yY Both seem to have the controllers placed before followed by a dot rather than after the domain name and the slash. Is there something that I'm misunderstanding here? Could do with some explanation as to how this works exactly not much luck finding out what this is called. Thanks :D