4x3 Aspect Ratio
4x3 (AKA 4:3, 12:9, 12x9 or 1.33:1) is an aspect ratio used in traditional television broadcast. It means the image is four units wide by three units high.
4x3 was the standard ratio used in early cinematic film production. It is rumoured that theatrical widescreen ratios were developed in part as a response to television. Film producers needed something to keep theatrical films superior to television, and widescreen did the job.
In modern times, 4x3 has been adopted as the aspect ratio for IMAX film production.
4x3 works well for certain types of program, e.g. talking heads. However it is not considered to be the best format for general use because the viewport is too narrow to simulate human vision. Widescreen aspect ratios are seen as more desirable, hence the gradual phasing out of 4x3 in favour of 16x9 for video and television.