fullscreen

As a noun overscan

is (television) the additional area around the four edges of a video image that is not normally seen by the viewer.

As an adjective fullscreen is

.

As adjectives the difference between fullscreen and letterbox

is that fullscreen is alternative form of lang=en while letterbox is transferred to home video formats while preserving the original aspect ratio, having black bars above and below the picture area.

As a noun letterbox is

a collection point for mail intended for onward delivery, a secure box or receptacle for this purpose.

As a verb letterbox is

to transfer a widescreen motion picture to home video formats while preserving the original aspect ratio, with the placing of black bars above and below the picture area.