Aspect Ratio describes the visual size of an entertainment medium such as television or film in terms of the image's width compared to its height.
For example, most older television sets in the United States have a ratio of 4:3 (1.33:1, known as "Academy Ratio"), meaning that the image you see is four units wide and three units tall. Widescreen televisions use 16:9 (1.78:1), but this format [...] [tvtropes.org]