An electromagnetic pulse (often referred to as an EM pulse) was a short-duration burst of broadband, high-intensity electromagnetic energy, capable of disrupting magnetic fields and producing current or voltage surges in conductive materials via magnetic induction.
In 2368, the gravitional wavefronts that destroyed the SS Vico in a black cluster created an EM pulse that flashed through the research vessel's computer banks. Nearly 83% of the ship's records and all the sensor logs were lost after this flashing. (TNG: "Hero Worship")
In 2369, Lieutenant Jadzia Dax sent an electromagnetic pulse via Deep Space 9's tractor beam to free Doctor Julian Bashir from the consciousness of the Kobliad criminal Rao Vantika. (DS9: "The Passenger")
The detection grid of the Imperial Hall on Ilari was vulnerable to a narrow-band EM pulse during its maintenance cycle every ten hours. In 2373, the USS Voyager considered using this weakness to storm the Hall and remove Tieran from Kes' body, but Tieran was already aware of the vulnerability and informed them that his soldiers would be waiting. (VOY: "Warlord")
In 2375, while proposing to destroy the Monac shipyards, Miles O'Brien suggested that they could have IKS Rotarran fire an EM pulse at the Monac star to trigger a solar plasma ejection. (DS9: "Shadows and Symbols")