What does "gearing" mean?

Gearing: (Mach.) The parts by which motion imparted to one portion of an engine or machine is transmitted to another, considered collectively; as, the valve gearing of locomotive engine; belt gearing; esp., a train of wheels for transmitting and varying motion in machinery. Frictional gearing. See under Frictional. -- Gearing chain, an endless chain transmitted motion from one sprocket wheel to another. See Illust. of Chain wheel. -- Spur gearing, gearing in which the teeth or cogs are ranged round either the concave or the convex surface (properly the latter) of a cylindrical wheel; -- for transmitting motion between parallel shafts, etc.