Mechanism and Machine

Mechanism:

A kinematic chain is an assembly of links ( or elements )  where links have relative motions and the motion of each link relative to each other is definite. A mechanism is obtained when one of the links in a kinematic chain is fixed.

In other words,

 A mechanism is a combination of rigid or restraining bodies so shaped and connected that they move upon each other with a definite relative motion.

Eg : Slider-crank mechanisms , gear mechanisms


Machine:

When two or more mechanisms are arranged in a special way to obtain a required motion and transfer of energy, it is called a machine.

Eg: IC engine, lathe

(A machine is anything that reduces human effort.. Aasaan bhasha me.. :D )