View source for Armor penetration

Armor penetration is a system by which you can ignore a percentage of your foe's armor value from the damage calculation of [[white damage]]. As white damage (or the damage done simply by your weapon swings) is the most consistent damage in the game, this is a very strong bonus to boost, albeit a rare one.

Armor penetration as a mechanic functions through armor resistance (resist armor) on the part of the attacker.