Electro Magnetic Pulse (EMP) effects by e.g. a nuclear explosion and pulse-generating devices may be comparable to geomagnetic disturbances. The resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges. Both EMP and Geomagnetic disturbances may seriously affect to undisturbed working of Critical (Information) Infrastructures.
Electromagnetic pulse (EMP) :
1. The electromagnetic radiation from a nuclear explosion caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the nuclear device or in a surrounding medium.
2. A broadband, high-intensity, short-duration burst of electromagnetic energy. 
Note: In the case of a nuclear detonation, the electromagnetic pulse consists of a continuous frequency spectrum. Most of the energy is distributed throughout the lower frequencies between 3 Hz and 30 kHz.
The term EMP means an electromagnetic pulse caused by a nuclear device or nonnuclear device, including such a pulse caused by an act of terrorism. 
HEMP: high altitude electromagnetic pulse
IEMI: intentional electromagnetic interference
NNEMP: non-nuclear EMP
- ↑ US Gov definition
- ↑ US Strategy for protecting and preparing the homeland against threats of EMP and Geomagnetic disturbances, DHS, October 2018