letterboxing

/ ˈlɛtəˌbɒksɪŋ /

noun

1. a method of formatting film that enables all of a wide-screen film to be transmitted on a television screen, resulting in a blank strip of screen above and below the picture
2. a type of treasure hunt in which a box, known as a letterbox , is hidden in a remote rural location and clues are provided as to its whereabouts