What does bracketing exposures mean?

I'm getting a nikon d90 and i was just curious to what that means, and what it does.

Added (1). How do you do it? I forgot to add that in…

Takes one 0EV, one -1EV, +1EV for as long as you hold down the shutter.

Bracketing is varying the shutter speed or aperture up and down to get a correct exposure, i.e. If you meter says:

1/500 F8, then bracketing for aperture would give you 1/500 F7.1 1/500 F8 and 1/500 F9

The main use is for HDR shots, where you change shutter speed by 1/2-1/3 stop increments to get 3-9 exposures to combine in post process.

It means that using your light meter, you use the recommended exposure and then take a second and third shot exposing over and under the exposure determined by the cameras light meter.

This technique is used in unusual lighting conditions where the light meter may be fooled or if you are taking a set of exposures you intend to later compile into an HDR image

A simple bracket could be this. Normal exposure, 1/500th second at f/8. Bracket under, 1/1000th second at f/8, bracket over, 1/125th second at f/8. These listed exposures are in one stop increments. The reason for using the same aperture is to assure that there's no depth of field shift if your goal is to make an HDR file

It means you take a series of shots, with different settings to slightly vary the exposure of each. It's done if you're unsure of what settings will produce the 'best' exposure, or commonly in HDR photography, where you want to combine a series of images of the same scene under, over and 'correctly' exposed to bring out highlight & shadow details.

When you get the D90 - look up AEB (auto exposure bracketing) in the menu. Using this in combination with a continuous shooting mode will allow you to quickly take a bracketed sequence.

What the others said, i will add its the shutter speed that is adjusted not the apperture as apperture will alter the depth of field of the image

to do it, meter your exposure in manual mode, take a shot, then change your shutter spped up and down to bracket the first exposure