An add-on domain is a new domain that is added on top of your main domain. It creates a sub directory within your main web hosting directory but can show a different web site. The add-on domain collects the information from the sub domain directory using the same space and bandwidth as your main account, however it won't have its own cpanel.
Add-on domain benefits
1. Create multiple domains/websites on the same web hosting account.
2. Save money and web space by using one hosting account instead of several hosting accounts.
3. The add-on domain shares all the same resources (disk space, bandwidth...) with your main site.
4. The add-on domain has its own FTP manager, site stats, cgi-bin which is created automatically.
5. Upload all pages, images, scripts, forums etc to your add-on domain directory.
6. Access your add-on domain using several web site addresses