Source : Free On-Line Dictionary of Computing

flip-flop
     
         A digital logic circuit that can be in one of two
        states which it switches (or "{toggles}") between under
        control of its inputs.  It can thus be considered as a one bit
        memory.  Three types of flip-flop are common: the {SR
        flip-flop}, the {JK flip-flop} and the {D-type flip-flop} (or
        {latch}).
     
        Early literature refers to the "Eccles-Jordan circuit" and the
        "Eccles-Jordan binary counter", using two {vacuum tubes} as
        the active (amplifying) elements for each {bit} of information
        storage.  Later implementations using {bipolar transistors}
        could operate at up to 20 million state transitions per second
        as early as 1963.
     
        (1995-11-11)