The hosted domains feature of a hosting account indicates the amount of registered domain names which you could add in the very same account. Registering a domain and hosting it are two different services even though many people consider them to be the very same thing. While the registration means that you become the owner of a given domain, the hosting aspect is what in fact enables you to have a site considering that this is where your data and e-mails will be. Since these are 2 independent services, you can register a new domain with one company and host it with another one by changing its name servers (DNS) - the domain name is going to work in the exact same way just as if it was registered and hosted using the same company. It's also very important to know that changing the hosting means pointing the domain name to a different company and not transferring it.