A machine is any mechanical or organic device that transmits or modifies energy to perform or assist in the performance of tasks. It normally requires an input as a trigger, and transmits the modified energy to an output, which performs the desired task.

Humans have used mechanisms and machines to amplify their abilities since before written records were available. The primary difference between simple tools and simple mechanisms or machines is a power source and a somewhat independent operation. The term machine generally applies to an assembly of parts operating together to perform work. Generally these devices decrease the intensity of an applied force, altering the direction of the force or transforming one form of motion or energy into another.
(From Wikipedia, the free encyclopedia.)