A lens with a maximum wide aperture (f/1.4, f/2, f/2.8) allowing it to gather more light than a "slow lens" which has a less wide maximum aperture (f/3.5, f/4 and smaller).
is a lens which can gather and transmit more light to the camera. A fast lens has a larger iris opening and therefore a smaller F-stop.
A lens that has an aperture that opens particularly wide, making it able to gather more light than a slower lens at its widest aperture.
A lens with a wide maximum aperture (f2.8 is a fast lens in a 35mm telephoto design). Often used in low light situations or when a fast shutter speeds are always required.
A lens with a wide maximum aperture (e.g. f/1.7 or f/2.8), allowing in a large amount of light. While they perform well in low light, fast lenses tend to be large and expensive. Lenses with small maximum apertures (e.g. f/5.6 or f/8) are called slow lenses.
A lens that has a wider aperture opening (meaning a lower f-stop number) means it can let in more light than a lens with a higher minimum f-stop number. Therefore a 2.8 lens is faster than a 5.6 lens.
A lens with a wide aperture that lets a lot of light through. Fast lenses are especially useful in low light situations and when you want a very small depth of field.
