Parts of a sail
Foot
The bottom edge of a sail, running from tack to clew.
DutchOnderlijkour Dutch loft →
SpanishPujamenour Spanish loft →
The foot is the lower edge. On a mainsail it runs along the boom — either fed into a groove ("foot-bolted") or flying free above it ("loose-footed"), which lets you adjust the sail's lower shape with the outhaul more directly.
On a headsail the foot runs from the tack down near the deck to the clew, and its length together with the luff is what decides whether the sail is a jib or a genoa.
Dutch class rules measure the foot as onderlijk, and often also specify the onderlijkzwaartelijn — the foot median — because for a curved sail the straight-line foot alone doesn't pin the shape down.