A gear is a toothed wheel that meshes with other gears to transmit motion and power. Gears are used in many machines and devices, including cars, bicycles, clocks, and drills. A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or cavities machined on the part, or separate pegs inserted into it. In the latter case, the gear is usually called a cogwheel. A cog may be one of those pegsor the whole gear. Two or more meshing gears are called a gear train.