Source : Free On-Line Dictionary of Computing

munching squares
     
        A {display hack} dating back to the {PDP-1} (ca. 1962,
        reportedly discovered by Jackson Wright), which employs a
        trivial computation (repeatedly plotting the graph Y = X XOR T
        for successive values of T - see {HAKMEM} items 146--148) to
        produce an impressive display of moving and growing squares
        that devour the screen.  The initial value of T is treated as
        a parameter, which, when well-chosen, can produce amazing
        effects.  Some of these, later (re)discovered on the {LISP
        Machine}, have been christened "munching triangles" (try AND
        for XOR and toggling points instead of plotting them),
        "munching w's", and "munching mazes".  More generally, suppose
        a graphics program produces an impressive and ever-changing
        display of some basic form, foo, on a display terminal, and
        does it using a relatively simple program; then the program
        (or the resulting display) is likely to be referred to as
        "munching foos".  [This is a good example of the use of the
        word {foo} as a {metasyntactic variable}.]