One of the simple machines; a sheave, a wheel with a grooved rim, in which a pulled rope or chain lifts an object (more useful when two or more pulleys are used together, as in a block and tackle arrangement, such that a small force moving through a greater distance can exert a larger force through a smaller distance).
User Defined Definitions
"a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope"