In the real world it is a pulse of electro-magnetic energy that can destroy and disrupt electronic devices. It is generated by an atomic bomb at high altitude or a special missle that the US military has developed. but in World of Warcraft, it is a power of a [[w:c:wow:#|Personal Electromagnetic Pulse Generator]] made by high level [[w:c:wow:#|engineer]]s. It stuns {{ww|mechanical} mobs briefly.