A "surge" is a transient wave of current, voltage or both in an electric circuit. Be aware that "surge" and "power surge" carry a layman’s connotation of almost any type of power disturbance, which differs from technical definition. Within the electrical standards community, the term ‘power surge’ approaches nebulous, inviting further information. "Surge" is more formally defined as a transient overvoltage or transient sub-cycle event, and not as an event that increases power frequency voltage for multiple cycles. Multi-cycle overvoltage events are more aptly named temporary overvoltages (TOVs), designating a similar sounding, but substantially different power anomaly. As an oversimplification, surges are caused by switching or lightning disturbances.
To learn more about surge protection watch this new video "What is a Power Surge?" from our residential division, surgeassure, and check out these surge protection FAQ's.