Also letter box. Chiefly British. a public or private mailbox.
Digital Technology, Television. a technique for displaying a wide-screen film or landscape video on a narrower screen by reducing its size but retaining the aspect ratio, with black bands filling the screen above and below the picture (often used attributively):letterbox videos.Compare pan and scan, pillarbox(def 1).

verb (used with object)

Digital Technology, Television. to display (a film or video) by using the letterbox technique.

Origin of letterbox

First recorded in 1765–75; letter1 + box1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for letterboxing



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
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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012