Parked domains are Alias of your main domain and allows 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. This is used usually to point different domains extensions to the same main website, for example .org, .net, etc. domains pointing to your main .com domain/site.
When you park a domain in your account you can create independent e-mail accounts based in the parked domain.
Note: This feature must be enabled for your hosting account before you can use it. Parked domains will not be functional unless the domain name is registered with a valid registrar and configured to point to our nameservers. This must be done before you attempt to park the domain in your cPanel.