Electromagnetic pulse damage - sometimes only called pulse damage, commonly abbreviated EMP or just EM damage - is one of the 8 damage types in the game. It includes damage from "intense magnetic fields".
EMP Damage is pure energy damage, which disrupts electrical systems. EMP damage is totally ineffective against Health in Biological Lifeforms, however, it does cause some damage against Armor. EMP damage, however, is the best damage against all Mechanical Lifeforms and Shields.
EMP critical hits will also temporarily stop armor regen. [Deployment 8]
For more detailed information about the effects of damage, see:damage type