Movies are filmed in various resolutions. Each resolution has it's own aspect ratio:
4:3 (To fit the old style CRT TVs)
16:9 or 16:10 (two common wide-screen formats)
2.85:1 (often used in high-end/non I-Max theaters).
If the native resolution of your TV does not match the aspect ratio of the movie you are viewing, you'll see black bars either on top and bottom, both left and right, or all around the displayed image.
-Wolf sends