'Bracketing' used loosely is the concept of varying a parameter both ways to hopefully 'get one of them right'.
Depending on situation, you can bracket exposure, aperture, shutter speed, ISO, white balance, focussing, and just about any adjustable parameter.
Of course, if you combine parameters, you'd need to shoot a lot. For example if i want exposure at -1, 0, +1 and also at three different white balances, that'll be 9 shots. If i throw in 5 focus positions, it'll be 45 shots. If i want it in 2 ISOs, then it'll 90 shots. Bracket wisely.
Most bracketing is done at the camera, though some, like white balance, can be bracketed at the computer for pictures shot in RAW mode.