White balance

White balance (WB)is parameter that helps us determine light temperature, apropos to adjust it as close as possible to ideal state in which on photography we get colors matching those in reality. Problems with determining WB incur because of the fact that not all light sources have the same temperature expressed in Kelvins, so under different kind of illumination we get different preview of White, but other colors too. To adjust WB means adjusting camera that under certain light white color really is shown as white.
Light source heat examples:

Candle flame 1500K
Heated (glowing) object 3000K
Sun rising and sun falling 3500K
Noon sun, Flash 5500K
Intense sun, clear sky 6000K
Cloudy sky, shadows 7000K
Blue sky 9000K
Most of digital cameras offer options of setting to predefined preferences, and more expensive and advanced cameras have custom WB option too, with which we can adjust WB ourselves in every moment by taking some white object and using it as a white reference to adjust the camera.