What is an alias domain?
The domain alias section in cPanel allows you to point different versions of your primary domain to the same content. This is also sometimes known as being a parked domain in cPanel.
For example, example.com might be your primary domain, but you might also wish to register example.net, example.org, example.biz, etc… and point them all to your primary website. You can add any domain as an alias domain to point to your primary domain name, it does not have to be a variation of your primary domain.
You can add a parked domain in cPanel from the Domains section and selecting the Alias option and entering the domain name you wish to use an alias or parked domain.