Source : Free On-Line Dictionary of Computing

full-duplex
     
         (fdx, from {telegraphy}) 1. A type of
        {duplex} communications channel which carries data in both
        directions at once.
     
        On purely {digital} connections, full-duplex communication
        requires two pairs of wires.  On {analog} networks or in
        digital networks using carriers, it is achieved by dividing
        the {bandwidth} of the line into two frequencies, one for
        sending, and the other for receiving.
     
        2. An obsolete term for {remote echo}.
     
        Compare {simplex}, {half-duplex}, {double-duplex}.
     
        (2001-07-21)