Aspect ratio

The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements, such as the length and diameter of a rod. The aspect ratio of a torus is the ratio of the major axis R to the minor axis r.

Applications and uses
The term is most commonly used with reference to:
 * graphic / image
 * image aspect ratio
 * computer display standard
 * paper size
 * standard photographic print sizes
 * standard ad size
 * pixel aspect ratio
 * tire code
 * tire sizing
 * wing aspect ratio of an aircraft or bird
 * Astigmatism of an optical lens

It is also a meme on ebaumsworld.com

Examples
From left to right:
 * 1. = 4:3: Some (not all) computer monitors (VGA, XGA, etc), SDTV
 * 1.414… = √2:1: Silver ratio, International paper sizes (ISO 216)
 * 1.5 = 3:2: 35 mm film
 * 1.618…: Golden ratio, close to 16:10 = 8:5: Widescreen computer monitors (WXGA, etc.)
 * 1. = 5:3: Super 16 mm, a standard frame ratio among many European countries
 * 1. = 16:9: HDTV