Wikipedia: Pan and scan

Copying widescreen film images to video within the proportions of an ordinary video screen.

A broadcast TV image had, through the 1980's, roughly the shape of a frame of 35mm film: a width 1.25 times the height. To broadcast a widescreen film, it is necessary to make a new negative from the original widescreen elements. One way to do so is to make a "letterbox" print; another is to "pan and scan" the negative.

During the "pan and scan" process, an operator selects the parts of the widescreen composition that seem to be significant and makes sure they are copied--"scanning." When the important action shifts to a new position in the frame, the operator moves the scanner to follow it, creating the effect of a pan shot.

This method allows the maximum resolution of the image, since it uses all the available video scan lines. But it severely alters compositions and therefore dramatic effects--for instance, in Jaws, the shark can be seen approaching for several seconds more in the widescreen version than in the pan and scan. The result can also be a bit jarring, especially in shots with significant detail on both sides of the frame: the operator must either go to a two-shot format, lose some of the image, or make several abrupt pans.

Once television revenues became important to the success of theatrical films, cameramen began to work for compositions that would keep the vital information within the "TV safe area" of the frame. Yet some directors still balk at the use of "pan and scan" version of their movies; for instance Steven Spielberg initially refused to release a pan and scan version of Raiders of the Lost Ark, but eventually gave in; Woody Allen refused altogether to release one of Manhattan and the letterboxed version is in fact the only version available on VHS and DVD.