Which type of reef forms parallel to the shoreline but is separated from an island by a lagoon?

This would be fringing reefs. These reef systems grow near to the coastline as well as around islands and large continents. They are generally separated from the shore via shallow lagoons. They are the most common type of reef system on the planet. They are similar to Barrier reefs which also grow parallel to coastlines, but barrier systems are separated by deeper and much wider lagoons.