When a mechanical switch or relay closes, the switch elements will often bounce, even if only briefly, before making final contact. This is of consequence if downstream elements are sensitive to the switching transients. A contact debouncing circuit is often used to remove the transients.

is the intermittent opening of closed contacts occurring after initial contact actuation or closure of the contacts due to mechanical rebound, or mechanical shock or vibration transmitted through the [..]

The tendency for butt action contacts to bounce apart as they come together. The bouncing action can prolong and arc, or open and close the circuit very quickly several times before coming to a closed [..]

Oscillation of the movable contact upon closure of the circuit.

The intermittent and usually undesired opening of mechanical relay contacts during closure, or closing of contacts during opening. Contact bounce period depends upon the type of relay and varies from [..]