An add-on domain is a fully functional domain that can be created from your cPanel. Once it's created it will have its own email, and its own folder from within the public_html directory.
Add-on domain URLs look like www.example.com Subdomain URLs look like forum.domain.com, cat.domain.com, etc. domain.com the www is replaced with anything you want. Parked domains are a placeholder site. You park it on top of another site, and it becomes a single page of the site you park it on.
