What is an addon domain?

Simply put that is an additional domain that you can use from the same Cpanel account. This can only be used with Maia5 accounts. Addon domains reside in folders inside your public_html folder. So the structure is : your primary domain's files are under public_html and your addon domain files are under public_html/domainname/. You can create emails, install scripts from Fantastico, create aliases and pretty much do everything you want with addon domains (Cpanel has a drop down menu where you can choose the domain name).

Important - if you want to add an addon domain please make sure you update your nameservers to the ones in the Welcome email before you add it - otherwise you'll get an error.