Bracketing is the taking of several photographs of a scene where different amounts of light reach the sensor.
Normally, as you change the shutter speed, the lens opening will change as well.
Or, as you change the lens opening, the shutter speed will change.
In both situations, the amount of light reaching the sensor is the same.
Each photograph will have the same brightness as the others.
However, when bracketing, the amount of light is varied to produce exposures each with a different brightness.
Bracketing is done when you're unsure of the best exposure.
For example, the shutter speed remains the same below, while the lens opening is varied.
The sensor is receiving different amounts of light, so the brightness of the photographs will vary as well.
Many cameras have automatic bracketing.
You can set your camera to take several different exposures.
You can also use exposure compensation, which is described in the next section.