A transient event is a short-lived burst of energy in a system caused by a sudden change of state. The source of the transient energy may be an internal event or a nearby event. The energy then couples to other parts of the system, typically appearing as a short burst of oscillation.
In electrical and electronic engineering such electromagnetic pulses (EMP) occur internally as the result of the operation of switching devices. Engineers use voltage regulators and surge protectors to prevent transients in electricity from affecting delicate equipment. External sources include lightning (LEMP), electrostatic discharge (ESD) and nuclear EMP (NEMP).
Within Electromagnetic compatibility testing, transients are deliberately administered to electronic equipment for testing their performance and resilience to transient interference. Many such tests administer the induced fast transient oscillation directly, in the form of a damped sine wave, rather than attempt to reproduce the original source. International standards define the magnitude and methods used to apply them.