A cay (/ˈkiː/ or /ˈkeɪ/), also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including in the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they can provide habitable and agricultural land for hundreds of thousands of people.