aspect ratio

The aspect ratio of a rectangular image display area is the ratio of the width of the rectangle to its height, expressed either as a ratio of coprime integers or a real number to 1. The two most commonly used aspect ratios are “fullscreen” (4:3 or 1.66:1) and “widescreen” (16:9 OR 2.35:1).

For example, a detail from Leonardo da Vinci’s Mona Lisa in a fullscreen aspect ration:

And in a widescreen aspect ratio: