Barrier island

A barrier islands is a ridge of sand that runs parallel to the main coast but is separated from it by a bay or lagoon.

1. A detached portion of a barrier beach between two inlets.
2. An offshore sand bar that rises above the mean high-water level, forming an island.
3. An sandy island formed on a barrier reef. ^[1].

This is the common definition for Barrier island, other definitions can be discussed in the article