A measure of visibility. A creature has total concealment when it is in a heavily obscured square, although it has only partial concealment against an enemy adjacent to it. Examples: Heavy fog, smoke, or foliage. Contrast with lightly obscured and totally obscured.
Published in Player's Handbook, page(s) 281, Player's Handbook 3, page(s) 220, Rules Compendium, page(s) 312, Monster Vault: Threats to the Nentir Vale, page(s) 123.