trapdoor

noun

1. 1.A hinged or sliding door set into a floor or ceiling.
2. 2.Such a trap set into the floor of a stage to allow fast exits and entrances.
3. 3.A secret method of obtaining access to a program or online system; a backdoor.
4. 4.The special information that permits the inverse of a trapdoor function to be easily computed.
5. 5.A door in a level for regulating the ventilating current; weather door.