To make a number of exposures in addition to the one consider to be "normal." Some of these exposures are to be greater than the "normal" and some less than the "normal." Bracketing significantly increases the chance of getting a exposure near perfect.

To make multiple exposures, some overexposed and some underexposed according to the indicated meter reading, used to control brightness, contrast, color and to ensure accurate exposure.

a series of images with a slight increase and decrease in exposure

or BRACKETING - Refers to taking a series of pictures, at least three, of the same subject with varying exposures - (1) the main exposure, which is presumed to be correct, but may not be; (2) an overexposure, generally of 1/2 or 1 stop's difference from the main exposure, and (3) an underexposure of 1/2, 1 or 2 stop's difference from the main exposure. The theory behind exposure bracketing is that the photographer may not be certain that the main exposure is best for the subject matter, and the subsequent exposures will provide "insurance" that at least one of the images will provide acceptable exposure. Sometimes, though, the photographer may simply want to see the effects of different exposures of a scene. The term "bracket" is analogous with grammatical brackets or parentheses, where they are located on either end of a phrase. "Bracketed" exposures fall on either side of the exposure that is presumed to be correct. The BROWNIE is the original consumer camera, developed by George Eastman in 1888.

to make sever exposures, some greater and some less than the exposure that is calculated to be correct.  Bracketing allows for error and permits selection of the best exposure after development.