表面略高于低潮线或与之同高的岩脉、珊瑚或沙地。 ——AAT-台湾  @zh

reef:A ridge or bank of rock, sand, shingle, etc., lying just above or just below the surface of the sea or another body of water, usually in such a way as to pose a hazard to shipping. In later use frequently spec.: a ridge of this kind formed of coral.——Oxford English Dictionary

reef:a line of sharp rocks, often made of coral, or a raised area of sand near the surface of the sea.——Longman Dictionary of Contemporary English  @zh

礁  @zh