Commonly known as HDR or "high dynamic range"
Exposure Bracketing - To illustrate this in more detail, let's look at an example.
Your camera tells you that for the scene you are photographing, you need a shutter speed of 125th/sec and an aperture of F8. With exposure bracketing, and depending on whether you are in Tv (shutter priority) or Av (aperture priority) mode, you can alter the shutter speed or aperture for each shot. Click each image for larger version (not on mobile).
So, if you are in aperture priority mode and set up for a 1 stop bracketing shot, your camera will adjust the shutter speed and you will end up with the following 3 exposures (as above);
The danger here, or at least something to be aware of, is that you are not in control of the shutter speed. This means that if the shutter speed goes too low to handhold during your exposure bracketing experiments, you may get camera shake so use a tripod if unsure.
If you are in shutter priority mode, your camera will adjust the aperture values and you will end up with the following;
Now you are not in control of the aperture and the effects of this are on the depth of field. As the aperture widens to allow more light in to overexpose, your depth of field decreases meaning that less of the shot will be in focus. As the aperture closes to underexpose, the depth of field increases. This means that more of the shot is in focus.
These are all important factors to consider when exposure bracketing. Each subtle change can alter the final "look and feel" of each image.
Exposure +/- Bracketing - Why/when would you use it?
You may come across a scene that has a wide "dynamic range". Meaning bright areas coupled with shaded or dark areas. In essence, you may get a "confused" meter reading from your camera.
Do you expose for the light area or dark? Do you use fill in flash or pull details from the dark areas in post processing?
If the range is quite broad and the scene is quite difficult, you could expose the first shot to a neutral area. Think about the white of a wedding dress against the black of a wedding suit for example. Not too bright and not too dark. Use a 1 or 2 stop bracketing exposure to ensure that one is correct.
Note: With weddings, I would first of all shoot RAW for security and peace of mind. I would take my reading from the dress first and foremost. I can then pull out other details during RAW processing. If you intend to try your hand at HDR photography, make sure you use a tripod so that each image is perfectly aligned with each other. This makes rendering the final image a lot easier.