Source : Free On-Line Dictionary of Computing

braille display
     
         (Or "refreshable braille display", "refreshable
        display") An electromechanical device that renders {braille}
        with tiny, independently controlled pins used to represent the
        state of dots in braille cells.  Each pin, in its "on" state,
        raises above the top of its hole in the screen; in its "off"
        state, it drops below the top of its hole.  Older systems used
        tiny solenoids to control the state of the pins; modern
        systems are {piezoelectric}.
     
        Typical dimensions of a braille display are 1 line of 40
        cells, each cell of two-by-eight dots.
     
        (1998-10-19)