The virtual work is the work done by a force (or a couple) on a body due to a small virtual (i.e., imaginary) displacement of the body. A virtual displacement is any arbitrary very small change in the position of a body. The displacement is only imagined, as the body is not actually displaced, for which the displacement is called virtual displacement. The product of the force and the virtual displacement in the direction of the force is called virtual work.
WORK OF FORCE
Consider a body that moves from a point A to B under the force F. If r denotes the position vector corresponding to point A, the small vector dr is called the displacement of the particle. The work done by the force F during the displacement dr