The ISO (International Standards Organisation) setting, controls the sensitivity of the camera’s sensor. It determines how much light is needed to capture an image. Increasing the ISO or sensitivity means that photographs can be taken in less light.
ISO like Apertures and Shutter Speeds is also measured in stops of light half or double the previous one.
The higher the number the more sensitive the sensor is for example 3200 high sensitivity.
100. 200. 400. 800. 1600. 3200. 6400

Example of ISO noise