What is an addon domain in cPanel?
An addon domain is a fully functional domain that can be created from within your control panel. Think of it as having multiple hosting packages all sharing the same control panel. You can give them email addresses, forwarders, and more the same way you do for your main domain on the account.
The addon domain will appear as a totally separate domain from your primary domain. There should be no evidence that your domain is an addon domain to incoming traffic when they visit your addon domain.
What is a Parked domain in cPanel?
Parked domains are additional domains which you host on your account. They will display the same website as your primary domain and do NOT have separate web statistics, but you can give the parked domain its own email boxes. Parked domains are often used by businesses that want to have more than one web address for advertising purposes.
For example, if you own domain1.com and it is the primary domain of your cPanel account, you can set up domain2.com as a parked domain and it will load the content of domain1.com. You will notice that although the content of domain1.com is loading in the browser, the address bar will display http://domain2.com/.