From Longman Business Dictionary
overbooko·ver·book /ˌəʊvəˈbʊkˌoʊvər-/ verb [intransitiveI, transitiveT]TRAVEL to sell more tickets for a plane, hotel etc than there are places availableThe airline offers cash as compensation for passengers when flights are overbooked.
—overbooking noun [uncountableU]the right to sue airlines for overbooking