letterbox

A letterbox is a slot or container for receiving mail—either in a door, mounted on a wall, or standing at the roadside.

In British usage, letterbox also refers to public collection boxes for outgoing mail.

As a verb, to letterbox means to distribute printed materials door-to-door.

In film and video, letterbox describes a widescreen format displayed with black bars above and below the image to preserve the original aspect ratio: The DVD includes both letterbox and fullscreen versions.