Aspect ratio refers to how the image appears on the screen based on how it was shot–the ratio of width (horizontal or top) to height (vertical or side) of a film frame, image, or screen.
Dating back to Thomas Edison’s equipment, 1.33:1 was for a long time the typical aspect ratio for film. The ratio 1.33:1, which was dubbed “Academy aperture” in 1932 by the Academy of Motion Picture Arts and Sciences, soon became the first standard ratio in film, and was used until the 1950s. (The ratio 1.33:1 is the same as the 4:3 ratio of a television screen.) During the 1950s, developments in wide-screen formats and aspect ratios were introduced, including 1.65:1 and higher. Other anamorphic systems, such as CinemaScope and Panavision, have an aspect ratio of 2.35:1, while Cinerama had a ratio of 2.77:1. The aspect ratio for 70-mm. films is 2.2:1, and letterboxed videos for wide-screen televisions usually have an aspect ratio of 1.77:1 (or 16:9). Standard 35-mm. films have an aspect ratio of 1.85:1 (normally 1.66:1 in Europe).