'Free will offerings' in the Bible

And thither ye shall bring your burnt-offerings, and your sacrifices, and your tithes, and heave-offerings of your hand, and your vows, and your free-will-offerings, and the firstlings of your herds, and of your flocks:

Thou mayest not eat within thy gates the tithe of thy corn, or of thy wine, or of thy oil, or the firstlings of thy herds or of thy flock, nor any of thy vows which thou vowest, nor thy free-will-offerings, or heave-offering of thy hand: