Parked domains
A parked domain, also known as an alias domain, points to the same website as your primary domain. Parked domains do not have web pages, separate index pages or folders associated with them.
By parking the domains under the primary hosting of your domain, they will display your primary website. In addition, the browser address bar will display the primary domain when a parked domain is used to access a website.
For example, if yourdomainname.com is your main website, you can purchase yourdomainname.net and assign it as a parked domain. Then, if a visitor were to go to yourdomainname.net, they would see the same website as if they had typed yourdomainname.com.
Addon domains
An addon domain is an independent domain and website entirely. Instead of being a domain within another, it is just a separate domain with its directory, code, and file structure. Meaning it points to its folder within public_html.
Addon domains allow you to host numerous websites within the same control panel. Of course, this domain requires you to register the new domain name before you can host it.
You can build and display a different website for your addon domain and create email addresses, forwarders, and more – the same way you would for your primary domain.