传动轮是许多种能够改变物理运动规模的机械零件之总称，它最重要的功能是透过两个以上不同直径的传动轮构成传动轮组，来改变力或力矩和转速。齿轮和滑轮是最常见的两种传动轮，但不限于此。

A transmission is a machine that consists of a power source and a power transmission system, which provides controlled application of the power. Often the term transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.