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