Definition of firewalls:
(n) :
(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.
(n) :
(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.
(v) :
(transitive, computer security) To protect with a firewall.
(v) :
(transitive, computer security) To block with a firewall.
(v) :
(intransitive, motor vehicles or aircraft, slang) To use maximum engine power or acceleration.
(n) :
(physics) A hypothetical phenomenon where an observer falling into a black hole encounters high-energy quanta at or near the event horizon.