Prevention of vibrations, responses, or resonances that would cause distortion if unchecked. Mechanical control is by friction; electrical control is by resistance.
Damping is a measure of a power amplifier's ability to control the back-emf motion of the loudspeaker cone after the signal disappears. The damping factor of a system is the ratio of the loudspeaker's nominal impedance to the total impedance driving it. 
A technique for stabilizing an electronic or mechanical device by eliminating unwanted or excessive oscillations. 
The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means.
Any effect, either deliberately engendered or inherent to a system, that tends to reduce the amplitude of oscillations of an oscillatory system.