Wildcard DNS makes it so that any subdomain redirects to your main website.
So, if anyone types randomjunk.domain.com or fakename.domain.com, it will go to http://domain.com/ .
You can add this record via cPanel by following these steps:
The process is mostly the same for an addon domain; however, there is one major difference:
If attempting to add a wild card subdomain for one of your addon domains, using the first set of steps will cause some issues with proper resolution. As always, if you have any questions, please contact our support agents and we'll be glad to assist you with getting this properly setup.