Parts of a sail
Clew
The aft bottom corner, where the sheet pulls.
DutchSchoothoekour Dutch loft →
SpanishPuño de escotaour Spanish loft →
The clew is the lower after corner, where foot and leech meet and where the sheet attaches. It is the corner that takes the working load every time the sail is trimmed, so it carries the biggest patch of reinforcement on the sail.
On a mainsail the clew also takes the outhaul, which pulls it aft along the boom to flatten the lower part of the sail.
Look at the load fan radiating out of the clew on the diagram: that pattern isn't decoration. Sail loads run corner-to-corner, and where the cloth is built to carry them along those lines rather than across them, it holds its shape longer. That is the whole idea behind a radial cut.