i) addon domain is a fully functional domain that can be created from within your control panel. Think of it as having multiple hosting packages all sharing the same control panel. You can give them email addresses, forwarders, and more the same way you do for your main domain on the account.
ii)Park Domain is a temporary Web page when they enter your domain name in a web browser. You can park your domain name to indicate you are reserving it until you create your website, find a hosting provider, or sell the domain name to a third party.
iii)Sub Domain are the third level domains that are used to organize your web site content.
Such as
http://www.yoursite.com

is the regular URL with out a subdomain.

http://products.yoursite.com