Source : Free On-Line Dictionary of Computing

hardware handshaking
     
         A technique for regulating the flow of data
        across an interface by means of signals carried on separate
        wires.
     
        A common example is the RTS (Request to Send) and CTS (Clear
        to Send) signals on an {EIA-232} {serial line}.
     
        The alternative, {software handshaking}, uses two special
        characters inserted into the data stream to carry the same
        information.
     
        (1995-01-23)