A group of two or more gears joined together. If the centre gear is used only to change the direction of rotation or to act as a "spacer", it is called an idler gear.

a combination of two or more interlocking gears used to transfer rotation from one spot to another

A gear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed.

(n) A mechanism consisting of two or more gears and used to transmit power. Normally, gear trains are used to do one or more of the following: increase speed, decrease speed, or change the direction of motion.

a typical local mechanism

The systems of gears which transmit power from the mainspring to the escapement.

Cluster of gearwheels forming a geared system.