This frame is underexposed. The image is too dark.
This frame is overexposed. Too much of the image is white.
This frame has good exposure.
Some camcorders let you change the exposure setting, which allows you to change how sensitive the CCD is to light. The higher the eposure, the brighter the picture, and the lower the exposure, the darker the picture. Usually, you want the entire range of light levels to fit between the darkest black and the lightest white that can be produced. This is often hard to do. If too much of the image is white, it is due to overexposure. If it is too dark, it is due to underexposure. Shutter speed also effects the exposure.