firewall

(architecture) A fireproof barrier used to prevent the spread of fire between or through buildings, structures, electrical substation transformers, or within an aircraft or vehicle.

(physics) A hypothetical phenomenon where an observer falling into a black hole encounters high-energy quanta at or near the event horizon.

(computer security) The software that monitors traffic in and out of a private network or a personal computer and allows or blocks such traffic depending on its perceived threat.