1) "The International Organization for Standardization (Organisation internationale de normalisation), widely known as ISO (pronounced /ˈɑɪsəʊ/), is an international-standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promulgates world-wide proprietary industrial and commercial standards. It is headquartered in Geneva, Switzerland." Source and further information: http://en.wikipedia.org/wiki/ISO 2) "Film speed is the measure of a photographic film's sensitivity to light. Film with lower sensitivity (lower ISO/ASA speed) requires a longer exposure and is thus called a slow film, while stock with higher sensitivity (higher ISO/ASA speed) can shoot the same scene with a shorter exposure and is called a fast film." "For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure." "The ISO standard 12232:2006 gives digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model." Source and further information: http://en.wikipedia.org/wiki/Film_speed#Digital_camera_ISO_speed_and_exposure_index