The hosted domains feature of a hosting account refers to the number of registered domains that you can add in the exact same account. Registering a domain and hosting it are two different services although many people consider them to be the exact same thing. While the registration means you become the owner of a specific domain, the hosting element is what actually allows you to have a web site as this is where your data and email messages will be. Because these are two separate services, it is possible to 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. It's also very important to know that changing the hosting means pointing the domain to a different company and not transferring it.