A setting on automatic cameras (as on the 'A' Series Canon cameras) which allows for intelligent setting of the aperture based on the shutter speed selected and the internal light-metre reading. For example, if I set the FD lens on my AE-1 Program to "A" and my shutter speed to 1/1000 of a second, if it's a cloudy day, it will automatically open the aperture enough to properly expose the film at the set shutter speed. A very handy setting when in a rush and unable to mess around with the f-stops.