THIS IS THE EXPOSURE TRIAGLE Aperture APERTURE IS a space through which light passes in an optical or photographic instrument, especially the variable opening by which light enters a camera.
shutter speed SHUTTER SPEED IS the nominal time for which a shutter is open at a given setting.
ISO ISO IS Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system.