The camera normally determines the optimal exposure given the semi-automatic or automatic settings selected by the user. There are times, however, when it is advantageous to capture images that are slightly under and over-exposed. This is called bracketing. The primary uses of bracketing include a fairly new technique called HDR. Depending on the camera, the user may select from 3 to 9 images. One image will have the optimal exposure while the rest will be underexposed and overexposed by an amount determined by the user (usually 1 stop). Each camera has a special setting normally located in the settings are of the menu where the user selects various elements to set.
Also see: HDR.