As far as I understood it is all of the yet to be delivered Airbus 320NEO that they are trying to off load. As they will not need the capacity growth coming from this.
Norwegian very proudly made the biggest airliner orders in European history, ordering bunch of 737MAX and a bunch of A320NEO. Reason for splitting between two manufacturers was that they could get the planes quicker that way. Some people doubted what they would do with all those aircraft, well now we know.