Is a specific behavior of letterboxed pictures. If a picture with a wide aspect ratio is letterboxed on a 4:3 monitor, and when the same image is shown on a widescreen monitor, the aspect ratio is unaltered, but the black bars are either reduced or removed, it is said to be anamorphic. This behavior is very common for widescreen DVD movies, fairly common for cut-scenes in PC games, but very uncommon in proper gameplay of PC games.
So that would mean that on a tripple Monitor settup you'd only have an image on the main Monitor and side monitors would be Black! Like The Witcher 2 was!
So Hor+ is the way games should be developped.