The hosted domains feature of a website hosting account refers to the amount of registered domain names that one could add within the same account. Registering a domain and hosting it are 2 completely different services although a lot of people consider them to be the exact same thing. While the registration ensures that you become the owner of a certain domain address, the hosting element is what actually allows you to have a web site since this is where your data and e-mails will be. As these are 2 separate services, it is possible to register a new domain with one company and host it with another by modifying its name servers (DNS) - the domain shall work in the exact same way as if it was registered and hosted with the same company. It's also important to know that changing the hosting means pointing the domain to a different company and not transferring it.