'Freewill Offering' 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 freewill 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 freewill offerings, or heave offering of thine hand:

And thou shalt keep the feast of weeks unto the LORD thy God with a tribute of a freewill offering of thine hand, which thou shalt give unto the LORD thy God, according as the LORD thy God hath blessed thee:

That which is gone out of thy lips thou shalt keep and perform; even a freewill offering, according as thou hast vowed unto the LORD thy God, which thou hast promised with thy mouth.