Emergency bulkhead

From Memory Alpha, the free Star Trek reference.

An emergency bulkhead is a bulkhead that is installed by a starship's isolation protocols to isolate a section of a ship in the event of a hull breach. (TNG: "Disaster")

Emergency bulkheads were installed in turboshafts and could be initiated to stop a turbolift from falling or to restrict access for unwanted passengers of a turbocar. (TNG: "Power Play")

Emergency bulkheads are also installed as a prerequisite for structural damage when a starship encounters a hostile environment or situation. (VOY: "Scorpion, Part II")