Subdomain:A subdomain is not a new domain but used to run a new website. It can be create using the existing domain by replacing or adding the prefix which will be used for a new website. Suppose you have a domain such as "www.yourdomain.com" and you want to create a subdomain then just replace "www" with your desired name as "download.yourdomain.com", "song.yourdomain.com", "helpdesk.yourdomain.com" and many more.
If your website does not contain www don't worry for that. It is not mendatory to have www as prefix of your website. To create a asubdomain you just need to give your desired name as the prefix of existing your domain.Addon Domain:
An addon domain is a fully new domain used to run a unique website. It can be create using the existing cpanel account but before that you need to register the domain. The files of your addon domain will share the same control panel and server.Parked Domain:
Parked domains are eqaul to primary domains(which you purchase with the hosting). It is not a unique website. Parked domain contains the same website name and the same contents of a website as primary domain. Only different is the suffix of the domain. Suppose your primary domain name is "yourdomain.com" then the name of your parked domain will be "yourdomain.net" or "yourdomain.org" or "yourdomain.info" etc. But the contents will be same as primary domain mentioned earlier.
