There is a concept of "root" domain at UCVHost, in which one account can have up to 12 root domains registered. Each "root" domain after the first one, called the "primary" domain, is an additional $5/month. All domains point to the same IP address of you virtual server.

The first "root" domain ("primary") that you assign to a virtual server is special because it is used to setup a mail server. All other "root" domains are added to that mail server as aliases.

Second level domains "mydomain.com" are usually added as "root" domain. Third-level domains can also be set as a "root" domain and UCVHost will charge $5/month for this domain.

The free sub-domains at UCVHost are those that are registered "underneath" any one of the "root" domains. For example, if "mydomain.com" is one of the "root" (and paid for) domains then "thirdlevel.mydomain.com" can be registered as a free third-level domain at UCVHost as well as "fourthlevel.thirdlevel.mydomain.com" . Up to 10 next and further level sub-domains can be registered under a single "root" domain which together with pre-registered "www", "ftp" and "mail" sub-domains brings the total number to 13.