A ring-shaped coral reef, island, or series of islets.

एक घेरा जैसा मूंगा रीफ, द्वीप, या द्वीपों की श्रृंखला।

English Usage: The atoll structure was formed over thousands of years.

Hindi Usage: अटॉल संरचना हजारों वर्षों में बनी।