Positive Passenger/Bag Matching (“PPBM”) was common in Europe before the United States, though programs developed here in the years following the the bombing of Pan Am flight 103. It means that the passenger and their bag has to travel on the same flight. If a passenger offloads from the aircraft, the baggage has to be removed also.
The idea there is that for security reasons you don’t want a passenger putting something on the aircraft (a checked bag) without tying their own life to its contents.