What is an Addon domain ?
Using the addon domains feature in cPanel, you can host multiple web sites under a single Shared Hosting account.
An addon domain is a domain that points to a subdirectory within your primary account. For example, if you own the example.com domain name, you can configure it as an addon domain so that its files are stored in your account. A visitor to the example.com web site cannot tell that it is hosted on the same server as your primary domain.
It is like having multiple hosting packages that all share the same cPanel. You can create email addresses, FTP accounts, Databases, all the same way you do for your primary domain of your the account. The only difference is that the files share the same control panel and that they all lie under your root directory.
Tip: To add an addon domain, the domain name must be already registered and configured to point to our shared hosting nameservers. If you need assistance with configuring an addon domain, please open a support ticket.
For instruction on how to create and addon domain, please follow this link:
How to Configure and Addon Domain