Thread:EmigaRaptor/@comment-83.112.114.175-20150312001719/@comment-24846733-20150312123302

It's the relationship between the lenghts of the sides of a screen, or video...

You should know how maths work, so http://www.fillthefunnel.com/wp-content/uploads/2014/05/4-3-OR-16-9.jpg here. Should be clear enough. :P