1. A part of a sail taken in or let out in regulating size
2. Reduction in sail area by reefing
3. A submerged ridge of rock or coral near the surface of the water.

1. To lower and bring partially inboard, as of a mast on a sailboat.
2. To reduce (a sail) by taking in a reef.
3. To roll up (a portion of a sail) in order to reduce its area.
4. To reduce area of a sail by rolling or folding part of it