The shape of a TV or video picture is referred to as the aspect ratio. The ratio is always given as the width to the height. In all older TV's the shape is almost square. This is known as the 4:3 aspect ratio. The more modern way of displaying a TV signal is in the 16:9 aspect ratio. This is more realistic as the human eye sees wider in it's peripheral vision (like the eye sees, from side to side) than from top to bottom. This is also the way that most films are recorded. People with conventional TV's will see black bars above and below the screen when displaying a 16:9(wide) image on a conventional 4:3(square) screen, whereas a 4:3 image displayed on a wide (16:9) screen will be stretched and people appear fatter.
4:3 on a 16:9 screen 4:3 stretched to fit a 16:9 screen Pan and Scan