The document discusses aperture, shutter speed, and ISO in photography. It defines aperture as the opening in a camera lens that controls the amount of light reaching the sensor or film. Shutter speed determines how long the shutter remains open when a photo is taken, with slower speeds allowing more light. ISO measures the sensitivity of the image sensor, with higher numbers allowing photos in darker conditions but resulting in grainier images. The document explains how aperture, shutter speed, and ISO work together to control the overall light and exposure of photographs.