Aspect ratio:

The width of the screen image in relation to its height.  The older 35 mm. standard aspect ratio was 1.33:1 or four to three.  The early television industry adopted this ratio.  Some common aspect ratios for wide-screen films are 1.66:1, 1.85:1, and 2.35:1.  See also Anamorphic, Letterbox, Nonanamorphic wide-screen, Pan-and-scan, Wide-screen film.