It can be both. "Enhanced for Widescreen TVs" = anamorphic as Max_Rebo said. That means the image will fill the screen left to right.
BUT
depending on the aspect ratio of the original film, you may end up with some letterbox lines at the top and bottom, as Moth3r said. 16x9=1.78:1 theatrical aspect ratio. Anything wider than that (more than 1.78) and you'll end up with letterbox lines, even if the disc is anamorphic.