Account Domain
The initial domain added to a host server. Also referred as the primary domain, first domain, main domain, server domain, host domain.
Additional Domain
Any domain added to a server after the account domain. Also referred as secondary domain, add-on domain, addon domain. It is a fully registered and separate domain, like the account domain, and has its own files and folders on the same server as the account domain. In reality, it is separate but is dependent on the account domain’s existence, due to the account domain’s ties to the server. Whereas, the account domain is not dependent on any additional domain’s existence.