ISO

Low ISO: 100

                                                                      High ISO: 1600

1. What is ISO: The measure of a digital camera sensor's sensitivity to light.
2. How does ISO work both technically (in camera) and visually (in photo). Visually the iso effects how grainy the photo is but technically the higher ISO you have a grainy picture but with a low ISO it is clear and soft looking.  
3. What is relationship to the exposure triangle? When you move the ISO you also have to adjust the shutter speed and aperture to have a good photo.