Addon domains allow you to host more than one unique website (such that have different content) on one account.
Example: domain1.com is the domain name you have signed up to be hosted by Joomlinux. Then you decide to host another unique website - domain2.com - on the same account. That is when you need an addon domain.
A similar case is when you wish a new domain name to point to a folder or a subdomain of your website.
Addon domains are considered upgrades at Joomlinux. They cost $30 per year.
