Domain name
Your domain name is like a name for your web site. It is unique and it is registered with a domain name registration company. For example, www.simplewebdesign.com.au is the name of this web site and it is registered with SmartyHost, a company which sells domain name registrations and web site hosting.
The .au Domain Administration web site has a list of organisations that are Accredited Registrars for .au domain names which you can use to register your unique domain name.
