The Great Barrier REEF is a large coral REEF system located off the coast of Queensland, Australia. It is the world's largest coral REEF system, composed of over 2, 900 individual reefs and 900 islands stretching for over 2, 300 kilometers. The term 'Great Barrier REEF' is often abbreviated to 'GBR' or 'GBRR'. The REEF is home to a wide variety of marine life, including over 1, 500 species of fish, 411 species of hard corals, and one-third of the world's soft coral species. The REEF is also an important habitat for endangered species such as the dugong and the large green turtle. The Great Barrier REEF is a popular tourist destination, with millions of visitors each year. The four-letter answer to the crossword clue is 'REEF'.