Source : Free On-Line Dictionary of Computing

firewall machine
     
         A dedicated gateway machine with special security
        precautions on it, used to service outside network, especially
        {Internet}, connections and dial-in lines.  The idea is to
        protect a cluster of more loosely administered machines hidden
        behind it from {crackers}.  The typical firewall is an
        inexpensive {microprocessor}-based {Unix} machine with no
        critical data, with modems and public network ports on it, but
        just one carefully watched connection back to the rest of the
        cluster.  The special precautions may include threat
        monitoring, {call-back}, and even a complete {iron box}
        keyable to particular incoming IDs or activity patterns.
     
        Firewalls often run {proxy gateways}.
     
        Synonym {flytrap}, {Venus flytrap}.
     
        (1997-06-08)