A pulley is a simple machine consisting of a WHEEL with a groove in its circumference that is used to lift or move heavy objects. The WHEEL is known as a 'sheave' and the groove is known as a 'HOIST'. A pulley is used to change the direction of a force, reduce the magnitude of a force, or increase the speed of an object. It is also used to transfer energy from one point to another. The term 'pulley' is derived from the Latin word 'pullus', which means 'little WHEEL'.