What is Aval?

Legal Definition
In French law. The guaranty of a bill of exchange; so called because usually placed at the foot or bottom (aval) of the bill. Story, Bills, §§ 394, 454. The act of subseribing one's signature at the bottom of a promissory note or of a bill of exchange; properly an act of suretyship, by the party signing, In favor of the party to whom the note or bill is given. 1 Low. Can. 221.
-- Black's Law Dictionary
Legal Definition
A guaranty of a negotiable paper.
-- Ballentine's Law Dictionary