UniPass is a legacy password system that has largely been superseded by the zPass system. There are a few UNSW online systems that still use it but none that are used in CSE.
Occasionally it might be needed if someone doesn't have a working zPass, for more information see the UNSW IT website for students or staff.
Importantly, incoming students do not get a zPass until after they have officially enrolled. They use a Unipass to log into myUNSW to complete enrolment for their course.