[zmth]

It is simply the horizontal dimension divided by the vertical and 4/3=1.33/1 or more simply just 1.33 was the main tv standard of which all tv's were made esp the cathode ray type and most all tv station broadcasts till around 2003 or so when some started changing to 16/9 which is now the official standard for digital tv though some are still mixed - like some of the older reruns etc. are 4/3 but the present trend is for more and more to go to the16/9 and an increasing percentage of the tv's sold today will be 16/9 rather than 4/3.