A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

கடற்காயல் அல்லது வாவி அல்லது களப்பு (lagoon) எனப்படுவது காயல் அல்லது உப்பங்கழி எனப்படும் கடல் சார்ந்த ஏரி ஆகும்.