Exposure bracketing is a common technique that photographers use to make sure that their photos are properly exposed. This is particularly useful when lighting conditions are less than optimal. When you use exposure bracketing, you take 3 pictures of the same scene with different exposure, white balance and flash settings. One picture will be taken with an aperture and shutter speed combination that your camera deems appropriate to expose the scene. Another picture will be taken where the scene is under-exposed (negative exposure compensation) and the final picture will over-expose (positive exposure compensation) the scene. The under-exposed and over-exposed photos can be taken within a -3 to +3 stop range, represented as EV.
Conveniently, most SLR cameras have an Auto Exposure Bracketing (AEB) feature that will automatically take the 3 pictures for you. You simply set the EV value and the camera will take a picture that it thinks is properly exposed, a picture that is slightly under-exposed and a picture that is slightly over-exposed.