is a number used to express the light sensitivity of the digital camera. ISO has its origins in film photography, where the ISO setting measured the sensitivity of a particular roll of film to light.
With a digital camera, you usually can shoot at a variety of ISO settings. Higher ISO settings allow you to shoot digital photos in low-light conditions, but such photos are more susceptible to noise and grainy images than photos shot at low ISO settings.
Also Known As: ISO settings, ISO sensitivity