What does "barrier reef" mean?

A reef separated from the adjacent coast by a channel or lagoon; a reef that forms a barrier between the open ocean and the waters of the shoreline.

Barrier reef

Common synonyms include: caribbean barrier reef, coastal reef, coral reef, marine reef, reef, reef barrier.

noun

noun ·Rare ·Advanced level

Noun

1
A reef separated from the adjacent coast by a channel or lagoon; a reef that forms a barrier between the open ocean and the waters of the shoreline.
"Ask anyone who's been there and they'll tell you the same thing - there's no surf in Tahiti. The reason they say is because this barrier reef."
2
a long coral reef near and parallel to the shore wordnet

"Ask anyone who's been there and they'll tell you the same thing - there's no surf in Tahiti. The reason they say is because this barrier reef."