Source : Free On-Line Dictionary of Computing

glass tty
     
        /glas T-T-Y/ or /glas ti'tee/ A terminal that has a display
        screen but which, because of hardware or software limitations,
        behaves like a teletype or some other printing terminal,
        thereby combining the disadvantages of both: like a printing
        terminal, it can't do fancy display hacks, and like a display
        terminal, it doesn't produce hard copy.  An example is the
        early "dumb" version of Lear-Siegler ADM 3 (without cursor
        control).  See {tube}, {tty}; compare {dumb terminal}, {smart
        terminal}.  See "{TV Typewriters}" for an interesting true
        story about a glass tty.