White Balance is the adjustment of light temperature to make the image look as natural as possible (what your eyes see).
Most cameras will have preset white balance modes as shown with these symbols:
Light temperature is measured in Kelvin. Here’s a chart that scales the various camera WB settings:
(Image by TheCareyAdventures.com)
Cameras are usually set to Auto WB by default which means the camera will automatically measure the temperature of the scene. Auto WB works well in most cases. If you’re shooting RAW, you can manually adjust white balance in Photoshop or Lightroom.