An add-on domain is a secondary domain name that points to a folder (subdirectory) within the main hosting account. It can be added from your cPanel.
www.seconddomain.com will show the files actually in www.maindomain.com/afolder/ while maindomain.com will be completely hidden
An add-on domain will act like a full account. You can create sub-domains, email accounts, and FTP accounts for your add-on domains directly from your cPanel. There will be no private cPanel logins for add-on domains.
Add-on domains is a paid add-on in most packages, but you can also order them directly from your admin panel.
Prices listed for add-on domains do NOT include domain name registration fees. You need to pay for the domain registration and you must point them to the same nameservers of your main domain.
How to add add-on domains:
You can register the addon domain direct from your super user admin area and choose the main domain to get your new domain's name servers preconfigured
Order the add-on domain features from your Administration Panel via:
Administration Panel >> Order addons (Space, bandwidth, SSL, etc.).
Add the domain as an add-on domain from cPanel via:
cPanel >> Addon domains
Click the link below to find out how to do that in cPanel, in detail: