A Nikon name for lenses that have a focusing motor built into the lens. The S stands for "Silent Wave Motor", an ultrasonic motor. It focuses quickly and very quietly, but not completely silently. Because the motor is in the lens, AF-S lenses can autofocus on Nikon cameras that have no focus motor in the body. Most AF-S lenses also let you turn the focus ring by hand at any time, without switching off autofocus.
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