reef

Great Barrier Reef, Queensland, Australia

submerged reef (rock)

reef; shoal rock

barrier reef

shallow reef; shoal

atoll

reef island

lagoon

(of a ship) to strike a reef; (fig.) to hit a snag

Niu'e Reef, disputed territory in the South China Sea, claimed by China, Vietnam and the Philippines, aka Whitsun Reef or Julian Felipe Reef

Lagoon Nebula, M8

Scarborough Shoal (Philippines' name for Huangyan Island)

Bikini Atoll in the Marshall Islands, former US nuclear test site in the Pacific