What Does Television Aspect Ratio Mean?
Television aspect ratio refers to the ratio of a television screen's length vs. height. From the time the television was introduced, 4:3 or 1.33:1 was the standard aspect ratio used by televisions, only losing popularity as it became cheaper to manufacture HDTVs with an aspect ratio of 16:9.
Techopedia Explains Television Aspect Ratio
Since the commercialization of the television in the 1940s, 4:3 or 1.33:1 was the standard aspect ratio. It was even used for the 35mm films of the silent era, and it was very close to the aspect ratio defined by the Academy of Motion Picture Arts and Sciences, which was 1.375:1 for the new innovation of optical sound-on-film. Because of this, movies shot on standard 35mm can be viewed satisfactorily on 4:3 televisions. It was only when cinema audience numbers dropped that Hollywood started to create various widescreen formats, starting with 1.85:1, in order to "enhance" the viewing experience and entice more customers.
Some cable television stations even today still broadcast in 4:3 standard resolution because the infrastructure has been around for so long and the size of the picture means that little bandwidth is consumed compared to 16:9 widescreen HD broadcasts.