Overscan occurs on your high definition LCD, plasma and projection TVs when the video image is enlarged slightly and the outer 3% is cropped off. Engadget HD has an extremely thorough explanation of overscan, but we’ll boil down the important points here for you.
Overscan is a remnant of CRT TV days when images needed to be enlarged slightly to ensure the quality of the image at the center of the screen. There is no real excuse for continuing the practice today other than, “that’s how it’s always been done.”
Because overscan occurs, some broadcasters don’t attempt to provide images that are clear at the edges, or they use that space to include information that might be useful in production.
The good news is you can compensate for overscan by adjusting the pixel mapping on your TV. Typically there is a control on your LCD, plasma or projection TV remote that allows you to manually adjust the picture size. You will want to look for a button on your remote labeled something such as “format,” “screen size,” “picture size” or “p size.” You can use this to toggle through your various screen settings to find the one where you get a full screen fit. Of course, you may not even notice or care that your picture is being blown up slightly. In which case, you can leave things well enough alone.