hidden

When a creature is hidden from an enemy, the creature is silent and invisible to that enemy. A creature normally uses the Stealth skill to become hidden. See also invisible.

Published in Monster Manual 2, page(s) 217, Player's Handbook 3, page(s) 221, Rules Compendium, page(s) 312, Monster Vault: Threats to the Nentir Vale, page(s) 123.