Letterboxing is the practice of transferring film shot in a widescreen aspect ratio to standard-width video formats while preserving the film's original aspect ratio. The resulting videographic image has mattes (black bars) above and below it; these mattes are part of each frame of the video signal. LBX or LTBX are identifying abbreviations for films and images thus formatted.
This article needs additional citations for verification. (December 2011)