Parts of a sail
Head
The top corner of a triangular sail, where the halyard lifts it.
DutchTophoek
SpanishPuño de drizaour Spanish loft →
The head is the top corner, where the halyard attaches. On a triangular sail it is a point where luff and leech meet; on a big full-batten mainsail it is often a small square "headboard" instead, spreading the halyard load and letting the roach carry right up to the top.
The head is a high-load corner: the whole hoisting force of the sail passes through it, so it gets reinforced with extra layers of cloth.
On a four-sided sail - gaff, gunter, lug or sprit - there is no single head. The top edge is held by a spar between two corners, the throat forward and the peak aft.