A coral reef island, also known as an ATOLL, is a ring-shaped island that is formed by coral reefs and other sedimentary rocks. It is typically found in tropical and subtropical waters, and is composed of coral, sand, and other organic material. The term 'ATOLL' comes from the Dhivehi language, which is spoken in the Maldives. Atolls are often home to a variety of marine life, including fish, turtles, and other aquatic creatures. They are also important for protecting coastlines from erosion and providing habitats for many species of birds.