The majority of billiard halls where you see a sign of pool balls or a rack of balls outside are called Dangu-jangs (billiard rooms). They almost never actually have any pool tables, instead having all carom/3 cushion tables. The following great places are exceptions and are focused on pool, or as Koreans call it, pocketball. Please inform me if there are any changes to this list via email or our facebook group!
The definitive guide to playing pool in Seoul!