letterbox
[ let-er-boks ]
/ ˈlɛt ərˌbɒks /
noun
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.