1. (Also called cold drop, cold-air drop. ) A region, or “pool,”of relatively cold air surrounded by warmer air; the opposite of a warm pool. This is usually applied to cold air of appreciable vertical extent that has been isolated in lower latitudes as part of the formation of a cut-off low. Cold pools are best identified as thickness minima on thickness charts. They are cyclonic-scale phenomena. 2. Any large-scale mass of cold air; a cold air mass or cold dome.