Source : Free On-Line Dictionary of Computing

spoofing
     
        A technique used to reduce network overhead, especially in
        {wide area network}s (WAN).
     
        Some network {protocol}s send frequent packets for management
        purposes.  These can be {routing} updates or {keep-alive}
        messages.  In a {WAN} this can introduce significant overhead,
        due to the typically smaller {bandwidth} of WAN connections.
     
        Spoofing reduces the required bandwidth by having devices,
        such as {bridge}s or {router}s, answer for the remote devices.
        This fools (spoofs) the {LAN} device into thinking the remote
        LAN is still connected, even though it's not.  The spoofing
        saves the WAN bandwidth, because no packet is ever sent out on
        the WAN.
     
        LAN {protocol}s today do not yet accommodate spoofing easily.
     
        ["Network Spoofing" by Jeffrey Fritz, BYTE, December 1994,
        pages 221 - 224].
     
        (1995-01-13)