Source : Webster's Revised Unabridged Dictionary (1913)

Aspect ratio \Aspect ratio\ (A["e]ronautics)
   The ratio of the long to the short side of an a["e]roplane,
   a["e]rocurve, or wing.

Source : WordNet®

aspect ratio
     n : the ratio of the width to the height of a tv picture

Source : Free On-Line Dictionary of Computing

aspect ratio
     
         The ratio of width to height of a {pixel}, {image},
        or {display screen}.  Square pixels (1:1) are considered
        preferable but displays are usually about 5:4.
     
        (1994-11-30)