An Australian Business Number (ABN) is a unique 11 digit number that identifies your business or organisation In Australia.
Being a rideshare driver generally means you are running a sole trader business, and you will need an ABN.
You can find out how to apply for an ABN through Airtax here.
Do I need to be GST-registered as a rideshare driver (e.g. through UberX)?
Yes, as a rideshare driver you are required to have an ABN which is registered for GST purposes. Usually there is a minimum turnover requirement of $75,000 for an ABN to be required to be registered for GST purposes, however this does not apply to rideshare drivers. You can find out how to register for GST purposes here.