The release of well pressure back through surface valves.

a rapid increase in n pressure downhole that occurs when the drill stem is lowered too fast or when the mud pump is brought up to speed after starting.

Condition of a vessel experiencing variable ahead speed.

characterized by great swelling waves or surges; "billowy storm clouds"; "the restless billowing sea"; "surging waves"

A pronounced fluctuation in output over a short period of time without deliberate change in operating conditions.