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.