Source : WordNet®

firewall
     n 1: the application of maximum thrust; "he slammed the throttle
          to the firewall"
     2: (computing) a security system consisting of a combination of
        hardware and software that limits the exposure of a
        computer or computer network to attack from crackers;
        commonly used on local area networks that are connected to
        the internet
     3: fireproof (or fire-resistant) wall designed to prevent the
        spread of fire through a building or a vehicle

Source : Free On-Line Dictionary of Computing

firewall
     
        1. {firewall code}.
     
        2. {firewall machine}.