Aperture priority

Aperture priority, often abbreviated A or Av (for aperture value) on a camera mode dial, is a mode on some cameras that allows the user to set a specific aperture value (f-number) while the camera selects a shutter speed to match it that will result in proper exposure based on the lighting conditions as measured by the camera's light meter. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting an appropriate aperture, or program mode where the camera selects both.