ISO is short for International Standards Organization – the main governing body that standardises sensitivity ratings for camera sensors.
It’s a a term that was carried over from film. When you change your ISO setting, you’re adjusting your camera’s sensitivity to light. ISO settings can be anywhere from 24 to 6,400 (or higher), and these numbers have a direct relationship with the device’s sensitivity, so a lower setting makes it less sensitive and a high setting makes it more so.
Along with shutter speed and aperture, ISO is one of the three factors that determine your picture’s exposure. Finding the right balance between these three settings is key to getting the perfect shot.