Pierce

Attacks usually have their damage reduced by the defense of the target. Armor piercing attacks first reduce the target's armor by the amount of pierce.

Pierce itself adds no damage.

Items with this trait: Broom, Crossbow, Flail, Lash, Mace, Pickaxe, Sling, Spear, Spiked club, Stone, Trident

The same tag on creatures means something else.