White Balance is an adjustment in electronic and film imaging that corrects for the colour balance of the lighting - so that white objects appear white, rather than coloured (for example) yellow when lit by tungsten filament lights, or excessively blue under sunlight.
Most digital cameras have automatic compensation for white balance, and the more advanced allow some manual adjustment - either to fixed settings or balancing on a particular image (e.g. a grey card). The white balance is adjusted by applying different weightings to the red, green and blue (RGB) components of the image coming from the sensor - based on the colour temperature.
Each type of colour film is designed for a particular colour temperature - and so has a particular white balance requirement for its lighting. Whilst most colour films are/were balanced for daylight, there were many films intended for use under domestic tungsten-filament light bulbs or slightly hotter studio lights. There were also films balanced for particular types of flashbulbs - although most later flashbulbs carried a blue coating to match their balance to daylight film.
Changing the white balance in a film system involves either adjusting the light source, or adding filters to the camera. Artificial lighting can be changed by adding filters, or controlling the temperature of the filaments through varying the electrical supply.