A Subdomain is a folder installed in your main domain. So if your main domain is www.yourdomain.com, then a subdomain of it would be www.yourdomain.com/subdomain. The subdomain could also be viewed as subdomain.yourdomain.com.

An Add-on domain is a separate domain that points to a folder within a website. So in effect, a Add-on domain points to a Subdomain. So if your main domain is www.yourdomain.com, you could set up an add-on domain such as www.addondomain.com to point to www.maindomain.com/subdomain/. Users visiting www.addondomain.com/file.html would actually be seeing www.maindomain.com/subdirectory/file.html, even though ‘www.addondomain.com/file.html’ would appear as the address in their browser.

A Parked domain just allows you to redirect people to your main domain. So if your main domain is www.yourdomain.com, but you also bought www.yourdomain.net, you can set www.yourdomain.net as a parked domain and anyone who goes to www.yourdomain.net will automatically be redirected to www.yourdomain.com.