- A shallow ridge of rock or coral.
- The portion of sail that can be folded out of use.
- To reduce the area of sail exposed to the wind.
16th century. From Old Norse, rif, of the same meaning.
That shallow area with rocks and coral is certainly fun to look at and swim around in, but is best avoided by ships. Water sports around a reef is also hazardous. I have some scars on my feet from surfing around some coral. James Bond also found out about the dangers of reefs the hard way, too. In the 1981 movie, For Your Eyes Only, the villain ties a rope around Bond and the girl and drags them behind a boat across a coral reef. Ouch!
Aside from all that it generally applies to sailors aboard sailing vessels.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport Museum.