A measure of visibility. A creature has partial concealment when it is in a lightly obscured square. Examples: Dim light, foliage, fog, smoke, and heavy rain or falling snow. Contrast with heavily obscured and totally obscured.
Published in Player's Handbook, page(s) 281, Player's Handbook 3, page(s) 221, Rules Compendium, page(s) 313, Monster Vault: Threats to the Nentir Vale, page(s) 124.