ADJ. having a vertical black stripe on the left and right side, such as a 4:3 television show when presented on a widescreen TV. Compare to letterbox.
Jill: Hey, if your fancy plasma TV is so awesome, then why does everyone look so fat when we watch your DVDs of Seinfeld? Like, even that clock on the wall is stretched out into an oval! What gives?
Jack: It's an old show. We could watch it in 4:3, but then it would be postcardbox, and those black bars drive me crazy.