Whenever a force (F) acts on a body and the body undergoes a displacement (x) in the direction of the force, then the work is said to be done.
Mathematically, Workdone = F.x = Force x Displacement.

The unit of work depends upon the unit of force and the displacement. In S.I. system of units, the practical unit of work is N-m. It is the work done by a force of 1 newton when it displaces a body through 1 metre. The work of 1 N-m is known as joule (briefly written as J), such that 1 N-m = 1 J.