A worm gear is a special toothed wheel gear with the shafts at right angles to each other. It consists of a worm, i.e. a screw with one or several threads and a worm wheel, i.e. a toothed wheel provided with a toothing to match the worm.

A worm gear is for instance used in cases where the number of revolutions has to be strongly reduced and where the compactness and/or the right angle between input and output is an advantage.