In plain English
The OAIC is where you report a data breach under the NDB scheme. It also publishes guidance on privacy best practice and can investigate complaints from individuals whose data has been mishandled.
Full definition
The OAIC is an independent statutory agency established under the Australian Information Commissioner Act 2010. It holds powers to investigate data breaches, conduct privacy assessments, and take enforcement action — including referring matters to the Federal Court for civil penalty orders.