'Freewill Offering' in the Bible

you will make an offering by fire for Yahweh from the cattle or from the flock, a burnt offering or a sacrifice to fulfill a vow, or as a freewill offering or at your feasts, to make a fragrance of appeasement for Yahweh.

" 'You will present these to Yahweh at your appointed time, in addition to your vows and your freewill offerings, for your burnt offerings and for you grain offerings and for your libations and for your fellowship offerings.'"