Aperture – An aperture is an adjustable opening in the lens that regulates how much light passes through. Aperture controls depth of field – how much of the image, from foreground to background, appears sharp. More info
Aperture priority – A mode (abbreviated AV) available on nearly all advanced and some point-and-shoot digital cameras that allows the user to set a specified aperture value (in f-stops). The camera automatically adjusts the shutter speed to achieve proper exposure for the selected aperture.