Definition of Lagoon:
A lagoon is a shallow body of water that is separated and protected from a larger body of water, usually the ocean, by natural barriers such as sandbars, barrier islands, or coral reefs.
Lagoons are typically coastal features found along shorelines where sediment deposition or coral growth creates a physical separation between the open sea and a calmer water body behind it. These water bodies often have brackish water due to the mixing of seawater and freshwater from rivers or rain.
Lagoons play an important ecological role by providing habitats for diverse marine life and acting as natural buffers protecting inland areas from storms and waves.
Conclusion:
Therefore, the correct term for a shallow, protected water body separated from the ocean by sandbars, barrier islands, or coral reefs is a lagoon.