The horrible process of displaying a motion picture in an aspect ratio the director never intended.

This most often happens to display a theatrically released film on your ordinary home television screen. The observant will notice these screens are two different sizes: usually with a ratio of 16:9 or 1.85:1 for a movie and a ratio of 4:3 for a television.

To fit a large image onto a small screen, you have two choices- shrink the image to fit everything (the widescreen option), or crop the image to fit (pan-and-scan). Sometimes this technique is blatantly obvious, as in the migrane-inducing sliding pan on Michael Keaton's movie, Multiplicity, or jarring, as in most cropped, artificially cut scene with two actors at extreme ends of the frame.

More details can be found at this copyrighted page: http://www.philipwilliams.com/widescreen/panscan.htm