UNDERSTANDING PARKED, ADD-ON AND SUB-DOMAINS
A PARKED DOMAIN is a domain name that leads to the same website as another domain name. the domain is, in essence, parked on top of another domain.
For example, suppose we have a domain name mysite.com. if we park mysite.org on top of the .com domain, a visitor to our site will be able to access the site from either the .com or .org address. The visitor won’t notice any difference in the website at all no matter which one he chooses.
An ADD-ON DOMAIN, on the other hand, is a domain that will display a completely different website. So if you pay to be able to host an add-on domain on your hosting account, you are basically being given permission to host another site in addition to your main website.
Best way to use Domain name and Sub-Domains
It is important to note that buying add-on domain or parked domain rights from your hosting provider doesn’t actually give you a domain name; it just gives you the ability to add that domain to your account. You’ll still have to pay the domain name, too.
SUB-DOMAINS, though, will work off your existing domain names. They can be sued for the same purpose as regular domain names; they just have an extra part in front.
WWW is actually considered a sub-domain, but one that is usually parked on top of the main domain.
Another example could be if you created two sub-domains dogs and cats on mypetsite.com. You’d visit those sub-domains in your browser using http://cats.mypetsite.com and http://dogs.mypetsite.com respectively.
You could set each sub-domain to go to its own website, or go to a secure section of the main mypetsite.com site.