Definitions for "Letterboxing"
When a 16:9 aspect ratio movie is shown on a regular television set, there are black bars on the top and bottom of the screen. This preserves the original shots of the movie.
A technique for fitting a rectangular image into a frame with a lesser width-to-height ratio, by shrinking it until its horizontal axis fits in the destination without cropping, at the expense of leaving unused display area area (in the form of bars, usually black, at the top and bottom of the screen).
The process of putting black bars at the top and bottom of the screen to change a 4:3 aspect ratio image to a wider aspect ratio image.
Similar to geocaching, its origins go back years before modern geocaching - where one uses a series of clues (instead of coordinates) to find a container. A carved stamp is in each letterbox for use in stamping your personal logbook. You then take your carved stamp and stamp the letterbox's log book.