In Event Manager, Unconfirmed Bookings occur when someone has filled out the Booking form with their information. The status 'Unconfirmed' simply means that it is up to the University whether or not they would like to allow this event to go ahead. This allows you to keep control of not only who is coming to your events, but also how many people are and also what event they are making a booking for.
There are four options you have when you receive an unconfirmed booking.
Confirm - Confirm the booking on this event
Move - Move this booking to another event and leave it unconfirmed
Move & Confirm - Move this booking onto another event and confirm it
Delete - Permanently delete this booking
Until the Unconfirmed Booking is either Confirmed or Moved & Confirmed, the booking will not be added as Booked on to the event and it will remain Unconfirmed until this is done.