To damp is to apply a
force to an oscillating body so as to reduce the
amplitude of its
oscillation. This will eventually stop its motion altogether. It is interesting to note that when an oscillating body decreases in
amplitude, its
frequency stays the same. It is completing the same number of oscillations per second as before, so it is moving more slowly.
One application of damping is in car suspensions. If cars were undamped they would oscillate pretty much continuously as soon as they hit anything like a stone or a speed bump, with obvious implications for comfort and safety. Cars are in practice damped to complete about one oscillation every time they start to wobble.