'Freewill Offering' in the Bible

and there you shall bring your burnt offerings, and your sacrifices, and your tithes, and the wave offering of your hand, and your vows, and your freewill offerings, and the firstborn of your herd and of your flock:

You may not eat within your gates the tithe of your grain, or of your new wine, or of your oil, or the firstborn of your herd or of your flock, nor any of your vows which you vow, nor your freewill offerings, nor the wave offering of your hand;

You shall keep the feast of weeks to Yahweh your God with a tribute of a freewill offering of your hand, which you shall give, according as Yahweh your God blesses you:

That which is gone out of your lips you shall observe and do; according as you have vowed to Yahweh your God, a freewill offering, which you have promised with your mouth.