Piercing is a suffix that can appear on Magic and Rare Items. It provides an Ignores Target's Defense bonus.
It doesn't start spawning on items until Item Level 25.
Ignores Target's Defense
Can appear on: Magic Items, Rare Items
Is available on: Katars, Daggers, Scepters, Staves, Wands
Monster Knockback — Bear
Ignore Target Defense — Piercing
Prevent Monster Heal — Vileness