"Unauthorised transactions" refers to actions or financial activities that are conducted without the permission or approval of the person or entity involved. Full definition
For more information see unauthorised transactions on your bank account and identity fraud. (moneysmart.gov.au)
For more information see unauthorised transactions on your bank account. (moneysmart.gov.au)
See ASIC's media release on Citibank refunds to customers when they were misled about their rights around unauthorised transactions. (moneysmart.gov.au)