fluctuation

Also from Answers.com... Back Pain What you can do to relieve your pain.

(oceanography) Wavelike motion of water. The variations of water-level height from mean sea level that are not due to tide-producing forces.
(science and technology) Variation, especially back and forth between successive values in a series of observations. Variation of data points about a smooth curve passing among them.

The characteristic feeling obtained by placing the fingers of one hand on one side of a swelling containing a fluid and, with the fingers of the other hand, tapping a distant point on the swelling. The sensation of wave motion transmitted from one hand to the other is an important sign of the presence of an abscess or the effusion of fluid into a joint.