A subdomain is a second website, with its own unique content, but without a new domain name. Instead, you use an existing domain name and change the www to something else. The subdomain would look something like: forums.example.com, blog.example.com, help.example.com.

An addon domain is a second website, with its own unique content. If you'd like more than one domain on your hosting account, this is the solution.

A parked domain is not a unique website. It is a masked forward to the primary domain name of your cPanel account, much like a website alias. For example, if you owned example.com and it was the primary domain of your cPanel account, you could set up exampletwo.com as a parked domain and it would load the content of example.com. The address bar would display http://example.com/.