From Lunarpages Web Hosting Wiki
A parked domain name would be one that is placed on top of a location. As an example, lets say I own both mydomain.com and mydomain.net. The domain mydomain.com is my main domain, but I can park mydomain.net on top of it so that anybody going to mydomain.com or mydomain.net will both be sent to the same server location where my web site is stored.
How to Park a Domain in cPanel
The first thing you will need to do is login to cPanel. From there scroll down to the Domains box and click on the Parked Domains icon. This will take you to the domain parking page. Domain pointers allow you to "point" or "park" additional domain names to your existing hosting account. This will allow users to also reach your website when entering the "parked" or "pointed" domain into their browsers.
Type the domain name you wish to park into the empty text box, then click on the Add Domain button. Now that domain you typed in will be parked on top of your primary domain name.
To see a listing of the domains currently parked on your account scroll to the bottom of the page:
To remove an parked domain, click on the Remove link on the same line as the domain. If you would like to redirect one of your parked domains, click on the Manage Redirection link.
Type in the URL that you would like the Parked Domain to redirect to and click the Save button.