Aspect Ratio

Aspect ratio
4:3 – old fashion small screened TV
16:9 – wide screen TV gives you a better viewing experience
pan and scan – cropping a shot
pillarboxing - a 4:3 shot onto a 16:9 shot the picture would be stretched.
letterboxing - a 16:9 shot onto a 4:3 shot you are left with 2 black lines on the bottom and top if your television.
When you pan and scan a wide screen shot suitable for a wide screen television (16:9) to a 4:3 television you lose a lot of the essence in the shot. E.g. action films, musicals.
Many films filmed today are shot in wide screen.