Auto Focus - Silent Wave (AF-S) is a type of focusing motor used in many of Nikon┐s AF-Nikkor lenses. The AF-S motor provides faster and quieter focusing. AF-S lenses also have an "A/M" mode selector which allows the user to switch from automatic to manual focus with almost no lag time.
Some older AF cameras are not fully compatible with the AF-S function. With these models, AF-S lenses will have to be focused manually. Incompatible models are: N60, N55, N8008/s, N6006, N5005, N4004 & N2020.