barrier reef A reef that trends parallel to a shore but is separated from it by a lagoon. The reef-building organisms build up the structure to approximately the low-tide level. One of the finest examples is the Great Barrier Reef which lies off the north-western coast of Australia: it extends for about 1900 km and is 30–160 km in width.

barrier reef Reef trending parallel to, but separated by a lagoon from, a shore. The reef-building organisms build up the structure to approximately the low tide level. One of the finest examples is the Great Barrier Reef which lies off the north-eastern coast of Australia: it extends for about 1900 km and is 30–160 km in width.

barrier reef Long, narrow coral reef lying some distance from, and roughly parallel to, the shore, and separated by a lagoon. Australia's Great Barrier Reef is the most famous.

http://www.reef.crc.org.au/aboutreef

bar·ri·er reef • n. a coral reef running parallel to the shore but separated from it by a channel of deep water.