Energy Armor Class (EAC)
Your Energy Armor Class (EAC) represents the defenses you have against attacks that only deal damage as a result of some kind of energy (such as acid, cold, electricity, fire, or sonic damage). When an opponent’s attack would deal only energy damage (if he is using, for example, a laser pistol), his attack roll result is compared to your EAC to determine whether he hits you. Some weapons and effects that use magical or exotic untyped energies might also target your EAC; the description of the weapon or effect tells you if this is the case.
Source
Core Rulebook pg. 240