Keyway
A slot used to assure the correct location in a mating connector.
Keying Slot or Polarizing Slot
A slot in a printed circuit board that polarizes it, thereby permitting it to be plugged into its mating receptacle with pins properly aligned, but preventing it from being reversed or plugged into any other receptacle.
Key
A device designed to assure that the coupling of two components can occur in only one position.
Kapton
Du Pont trade name for polyimide film.