Sails & rigs
Furling
Rolling a sail around a stay, foil, boom or mast so it can be stored or reefed.
Furling means rolling a sail away instead of dropping it and flaking it. A headsail usually rolls around a foil on the forestay; some mains roll into the mast or around the boom. In all cases the idea is the same: the sail is controlled by a drum, line and rotating spar or foil.
Furling is storage. Reefing is sailing with less area. The two overlap because many furling headsails are used partly rolled, but the shape is never as clean as a purpose-cut smaller sail. As the roll grows, the draft moves and the entry gets rounder.
A furling sail also needs the right construction: luff tape that fits the foil, a UV strip on the exposed edge, and enough reinforcement to tolerate being rolled tightly thousands of times.