The automatic white balance setting controls the automatic adjustment of the light source’s color temperature, which will adjust the picture’s color to maintain the “best” image. It keeps white objects white on the CCTV camera’s output, basically. Some security cameras offer multiple AWB settings. These cameras usually come with a chart that explains how to set the switches to get the desired results. This setting is usually fine to leave on, unless your security camera is displaying colors incorrectly.

For more on white balance, check out Wikipedia’s Color Balance page.