Definition for Aspect Ratio
From Biology Forums Dictionary
The proportions of the frame, the ratio of the width to the height of the image area. The traditional aspect ratio for 35 mm. film is 1.33:1 and is known as Academy Aperture. For wide-screen processes such as Cinemascope, the aspect ratio may range from 1.65:1 to 2.55:1. All film gauges are wider than they are high, a factor affecting formal composition within the frame.