By Volodymyr Zablotskyy

Whenever you purchase a web-hosting plan, you may be allowed to have certain number of Sub-Domains, Parked Domains and Add-On Domains in your account. This number differs from one hosting provider to another, but generally speaking most of the providers offer you certain number of each and some even allow you to have unlimited number of domains and sub domains.
So what is the difference?
The difference lies in the way you access your websites.

Sub-domains.
When you create a sub-domain for your website you will be asked to point that sub-domain to a particular directory on your website. Let say that your website's URL is http://www.mysite.com and you installed a Bulletin Board application in a directory "forum", then the full URL to that directory will be www.mysite.com/forum. Now you can create a sub domain named "forum" which will point to the URL [http://www.mysite.com/forum]. Internet users will be able to access your website by using either http://forum.mysite.com or [http://www.mysite.com/forum].

Parked Domains.
Parked domains allow you to point two or more different domains to the same web page. Let us presume that you have following domains http://www.mysite.com, http://www.my-site.biz, [http://www.my-other-site.com]. If these domains are parked domains and pointing to the same web page, no matter what address an Internet user will type in their browser, he will arrive to the same web page.

Add-On Domains.
With add on domains you have an option of operating several different domains independent of each other. I showed in the above example domains http://www.mysite.com, http://www.my-site.biz, [http://www.my-other-site.com]. Will point Internet user to three different websites if these domains are designated as Add-On Domains.
Volodymmyr Zablotskyy
Writer for Web Hosting Review Blog

Article Source: http://EzineArticles.com/?expert=Volodymyr_Zablotskyy

Whenever you purchase a web-hosting plan, you may be allowed to have certain number of Sub-Domains, Parked Domains and Add-On Domains in your account. This number differs from one hosting provider to another, but generally speaking most of the providers offer you certain number of each and some even allow you to have unlimited number of domains and sub domains.

We get asked this question all the time. The answer is actually pretty straightforward:

Sub domain

Lets say your domain is mysite.com.
You install a Message Board and put in in a directory called mysite.com/board/.
You can turn the directory board into a sub-domain by adding it as a sub-domain from your Control Panel.
Now you can access your Message board as either mysite.com/board OR board.mysite.com
This costs you nothing and is free.

Parked Domain

You have two domains mysite.com and my-other-site.com.
mysite.com is the domain of your website and you want to add my-other-site.com.
You want them both to go to the same place. In other words, when someone types either www.mysite.com or www.my-other-site.com they will go to the same page(s) on your website.
In order to have additional parked domains you need to purchase them from a registry.
Register Parked domains here (open a new account if you don't have one registered)

Add-On Domains

You have two domains mysite.com and my-other-site.com.
You want the two domains to be totally separate/independent websites.
In order to have additional add-on domains you need to purchase them from a registry.
Register Add-on domains here (open a new account if you don't have one registered)
http://www.thejobware.com/2011/05/ten-sexiest-jobs.html

If these domains are parked domains and pointing to the same web page, no matter what address an Internet user will type in their browser, he will arrive to the same web page.

Whenever you purchase a web-hosting plan, you may be allowed to have certain number of Sub-Domains, Parked Domains and Add-On Domains in your account. This number differs from one hosting provider to another, but generally speaking most of the providers offer you certain number of each and some even allow you to have unlimited number of domains and sub domains.