To reduce the area of one or more sails while they are being used by winding them over a roller or tying them up at particular points. There's too much wind to be at full sail—it's dragging the whole boat to one side. I'll keep a steady course while you go and reef in the mainsail. We should be fine if we just reef in the jib, I think. The captain ordered us to reef in the sails before the storm hit.