I for ISO
ISO, in terms of the camera settings and use, is the measure of the sensitivity of the sensor. More the ISO number, more sensitive it is. More sensitive means more light gathering capacity with allows you more latitude while manipulating the other essential camera settings for the shot. But, there’s a trade off too. With increased sensitivity, there comes, increased noise. The camera software works upto a certain limit to suppress the noise, but then, it becomes a bargain between more light or more sharpness. Keeping a low ISO, is recommended for a crisp photo.