A device that transfers torque from the input shaft to the output shaft by means of a set of gears, changing the output rotation speed. The gearbox contains a set of gears on two shafts. The rotation of a gear on one shaft is transmitted to a gear on the other shaft. If this gear has fewer teeth, it spins faster than the input shaft, if it has more, it spins slower. By selecting the appropriate ratio of teeth on the gears, the desired output rotation frequency is achieved,

In wind turbines, a gearbox is used to change the slow rotation speed of the turbine to a higher speed that can be used by the generator to generate electricity.