CIMM DEFINITION: The width-to- height ratio of the picture frame. TV broadcasts at a 4:3 (1.33:1) aspect ratio; digital TV is broadcast with a 16:9 (1.78:1) ratio; and most feature films are shot in at least a 1.85:1 ratio. (Source: itvt.com/glossary)

NOTE – HDTV also uses 16:9 aspect ratio. (Source: CableLabs)