This is the username of the owner of the domain. If you leave it set to Automatic the name will be the same as the first part of the domain name or the entire domain. Alternately, you can select to enter a custom username of your choice.

This login will typically be able to login via SSH and FTP, and manage the virtual server via the web interface. The password for all these services will be whatever was entered in the Administration password field. An email address with this username will also be created in the virtual server if it has mail enabled.