The idea is as old as the leaf that turns to face the sun as it moves across the sky. Tracking devices provide a way of maximizing the incident light striking a collector. They come in numerous orientations and varieties to suite a wide range of needs. The most simple is called the single-axis tracker. As its name implies it rotates about a single axis of motion, which may be oriented different ways, in order to maximize efficiency. Dual axis trackers offer better accuracy, which may be required for some applications, and also increase efficiency, but are naturally slightly more complicated and expensive. Heliostats are a type of dual-axis tracker that instead of directly following the sun, follows it in such a way that the light gets reflected to the same stationary point as the sun moves across the sky. To do this the heliostat has to bisect the angle between the target and the source (the sun), so it only needs to move half as much.
A plant with leaves that turn to follow the sun is called a heliotrope, so we are going to say that a tracking device which stays oriented towards the sun is called a heliotropic tracker, and a device which reflects to a stationary point is a heliostatic tracker. These are the two basic types of tracking strategies.
Tracking devices require motors. The two main ways drive a tracking device with a motor are either with gears (rotational) or linear actuators. Geared systems, while very accurate are also very costly and not as strong as linear actuators.
For those interested in learning how to make their own tracker, here's a link to a series of articles that outlines the whole process and explains the theory using the ubiquitous bicycle frame as the basic foundation: DIY Dual-Axis Bicycle Frame Tracker.