- a broadened barrier beach, habitable in places, that provides a measure of protection for the mainland, as during hurricanes and tidal waves.
- A long, narrow sand island that is parallel to the mainland and serves to protect the coast from erosion. Barrier islands typically have dunes along the exposed outer side, zones of vegetation in the interior, and swampy areas along the inner lagoon.
Any low sandy island that is parallel to the mainland and protects it from storms. (See Cape Hatteras.)