It is a requirement of the Australian government that if you want to study in Australia, you must have a valid Overseas Student Health Care policy. These policies are commonly referred to as OSHC.
The provision of OSHC for students studying in Australia can only be done by health insurers who have signed the "Deed for the Provision of Overseas Student Health Care". The Deed sets out what the insurers must cover, and what they do not have to cover.
Only a small subset of the Australian health insurance market have signed the Deed and are officially able to provide OSHC cover. Currently, the only health insurers able to provide OSHC cover are:
If you would like to know more about Australian government requirements with regards to OSHC for students in Australia, you can find it on the Department of Health and Ageing website.