Focus Tracking refers to the mechanism on a camera that can calculate the speed of a moving subject in order to properly focus and position the camera’s lens to capture the subject. In simpler terms, the focus tracking feature allows photographers to take clear, sharp, focused photos of moving objects.
For this reason, focus tracking is popular among sports photographers or others who take pictures of high-speed events, such as lightning flashes. For example, a sports photographer may use focus tracking to take pictures of racing cars, running basketball players or fighting hockey players.
With focus tracking, a photographer can place his camera in a particular spot, turn on the focus tracking feature and allow the camera to accurately anticipate and photograph the ensuing action.
Without this feature, action shots would turnout blurry and unfocused.
Focus tracking is a mechanism primarily found on Nikon and Cannon cameras. In fact, Nikon currently produces the camera with the fastest focus tracking abilities (set at F5).