Iron skin is a Cabal Online skill learned by Warrior, Blader from class rank 4. Description as it appears in the game:
Increase Defense with the force
Classes that learn it
Other Warrior skills at rank 4
These unlock at the same class rank, so the same quest gives you all of them: Rolling Crash, Cascade Break, Charge, Force Kick, Magic Cannon, Stone Cannon, Aqua Cannon, Wind Cannon, Fire Cannon, Crystal Cannon, Lightning Cannon, Change Force (Magic), Change Force (Sword).
FAQ
What does Iron skin do in Cabal Online?
Increase Defense with the force
Which class learns Iron skin?
Iron skin is learned by Warrior, Blader. It unlocks at class rank 4.
How do I raise my class rank?
Through the class rank quests the game offers every few levels. Each rank opens new skills and, later on, the Battle Modes.