Pair of pulleys attached to usually parallel shafts and connected by an encircling flexible belt (band) that can serve to transmit and modify rotary motion from one shaft to the other.
Most belt drives consist of flat leather, rubber, or fabric belts running on cylindrical pulleys or of belts with a V-shaped cross section running on grooved pulleys. Another type of belt, used on some internal-combustion engines for connecting the crankshaft and camshafts, is the toothed (or timing) belt, a flat belt with evenly spaced transverse teeth that fit in matching grooves on the periphery of the pulley.