Electric(al) damage - sometimes also called energy damage - is one of the 8 damage types in the game. It includes damage from all electrical sources.
Electric Damage is most effective against Bane Soldiers and Machina, which lack the proper shielding against Electric damage. Some Natural Biological Lifeforms have resistances or immunities to Electrical damage.
It should not be mistaken for Electromagnetic Pulse (EMP) Damage. Stalkers, Technicians, Predators, Hunters, and Hominus Machina are just some of the enemies immune to Electrical damage.
For more detailed information about the effects of damage, see: damage type