Temporary Overvoltage (TOV)    IEEE and IEC

An oscillatory overvoltage, associated with switching or faults (for example, load rejection, single-phase faults) and/or nonlinearities (ferroresonance effects, harmonics), of relatively long duration, which is undamped or slightly damped.

Note The overvoltage may be undamped or weakly damped. In some cases its frequency may be several times lower or higher than power frequency.