Read the dictionary definition of reef. All definitions for this word.
1. one of several strips across a sail that can be taken in or rolled up to lessen the area of the sail that is exposed to the wind
2. a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese
3. a submerged ridge of rock or coral near the surface of the water
4. reduce (a sail) by taking in a reef
5. roll up (a portion of a sail) in order to reduce its area
6. lower and bring partially inboard
1. reef the sailboat's mast