A trapdoor is a door set into a floor or ceiling (depending on what side of the door one is on). A trapdoor could also be called a hatch. Hidden trapdoors occasionally appear in fiction, either as entrances to secret passageways, or as literal traps into which a hapless pedestrian may fall if he or she happens to stand on one.

In computing, a trapdoor is a hidden capability that allows access to a program or computer system. Also known as a backdoor.

The Trap Door is a British animated series.