The hosted domains feature of a web hosting account refers to the number of registered domains that you could add within the exact same account. Registering a domain address and hosting it are 2 different services even though many people consider them to be the exact same thing. While the registration signifies that you become the owner of a specific domain address, the hosting element is what really allows you to have a site because this is where your data and emails will be. As these are 2 separate services, it is possible to register a new domain address with one company and host it with another one by changing its name servers (DNS) - the domain shall work in the exact same way as if it was registered and hosted with the exact same company. Also, it is important to know that changing the hosting means pointing the domain name to another company and not transferring it.