The hosted domains feature of a web hosting account denotes the number of registered domain names which you can add within the same account. Registering a domain name and hosting it are two completely different services although many people consider them to be the exact same thing. While the registration means you become the owner of a certain domain, the hosting aspect is what in fact allows you to have a site as this is where your files and e-mails will be. As these are two independent services, you are able to register a new domain with one company and host it with another one by modifying its name servers (DNS) - the domain shall work in the exact same way as if it was registered and hosted using the same company. It's also important to know that changing the hosting means pointing the domain to another company and not transferring it.