"Getting bumped" is the common term most people use when they are denied boarding on a flight because there is no room for them on the plane even though they have a reservation. The Chinese Airlines sometimes "overbook" and sell more than 100% of a particular flight's seats because they know that some of the people with reservations won't show up for the flight. Sometimes everyone does show up and this means that there won't be enough seats to go around and someone must be left behind. Those left behind have been "bumped" from the flight and will have to take a later flight.