Different Domain Name Types
From Lunarpages Web Hosting Wiki
What is the difference between a subdomain, parked domain and addon domain? Each are unique ways for a visitor to make his or her way to your web site. What makes them different though?
A subdomain name points to a subfolder of the primary domain. For instance, cats.pets.com would point to a subfolder such as /cats under the primary domain of pets.com. Its content is separate from the main site so it can act like a separate site though usually it will have some relevance to the main site as you can see above.
A subdomain can also be used on our system to redirect to somewhere else and create a shorter way to get there. For instance, mymail.mydomain.com could be redirected to http://mydomain.com/webmail/horde/ to get to webmail easier and force the use of the Horde webmail client.
Unlimited subdomains come with each hosting account.
Parked Domains (Aliases)
A parked domain is an additional domain that points to the main directory of your account (sort of like an alias). You can park unlimited domains at no cost on both the Basic and Business plans.
A parked domain will resolve to your primary domain name.
Say your primary is domain1.com and you park domain2.com. In the address bar if you type domain2.com it will resolve to domain1.com but in the address bar you will see domain2.com. This is a parked domain.
An add-on domain allows you to run a separate web site from your primary domain. When you create an add-on domain it makes a folder in your /public_html/ folder and you upload the site content into that folder.
So, essentially you are running 2 separate sites, separate content, off one account.
The Basic plan and Business plan both come with unlimited add-on domains included. This does not include domain registration.
Please note: You must own the domain/site yourself. Adding domains and sites that you do not own on our shared plans is against our TOS. Please also be sure to change the nameservers at your current registrar for domains you are adding or parking to use the same nameservers as your primary domain is. The nameservers are provided in your Critical Account Information email we sent on signup, and as seen in your CAP panel. Changes take 24-72 hours to propagate.