The hosted domains feature of a web hosting account refers to the number of registered domains that you could include in the same account. Registering a domain name and hosting it are 2 completely different services although many people consider them to be the exact same thing. While the registration means that you become the owner of a certain domain name, the hosting part is what in fact enables you to have a website as this is where your data and emails will be. Since these are two different services, you can register a new domain address with one company and host it with another by modifying its name servers (DNS) - the domain address is going to work in the exact same way as if it was registered and hosted using the same company. It's also very important to know that changing the hosting means directing the domain name to another company and not transferring it.