What is vibration ?

When something oscillates about a static position it can be said to
vibrate. The vibration of a speaker diaphragm produces sound, but
usually vibration is undesirable. Common examples of unwanted vibration
are the movement of a building near a railway line when a train passes,
or the vibration of the floor caused by a washing machine or spin
dryer. Floor vibration can be reduced with vibration isolators; however
there is often a penalty to pay in the form of a slight increase in the
machinery vibration and its consequent deterioration.