A freewill offering refers to a sacrifice voluntarily offered to God out of a grateful heart. It is one of the peace offerings, and all instances in the Bible referred to as "voluntary sacrifices" can be understood as this freewill offering.
Leviticus 7:11If he offers it for a thanksgiving, then he shall offer with the sacrifice of thanksgiving unleavened cakes mixed with oil, and unleavened wafers anointed with oil, and cakes mixed with oil.Leviticus 7:12He shall offer his offering with the sacrifice of his peace offerings for thanksgiving with cakes of leavened bread.Leviticus 7:13Of it he shall offer one out of each offering for a heave offering to Yahweh. It shall be the priest’s who sprinkles the blood of the peace offerings.Leviticus 7:14The flesh of the sacrifice of his peace offerings for thanksgiving shall be eaten on the day of his offering. He shall not leave any of it until the morning.Leviticus 7:15“ ‘But if the sacrifice of his offering is a vow, or a free will offering, it shall be eaten on the day that he offers his sacrifice. On the next day what remains of it shall be eaten,Leviticus 7:16but what remains of the meat of the sacrifice on the third day shall be burned with fire.
Numbers 15:3then he who offers his offering shall offer to Yahweh a meal offering of one tenth of an ephah of fine flour mixed with one fourth of a hin of oil.Numbers 15:4You shall prepare wine for the drink offering, one fourth of a hin, with the burnt offering or for the sacrifice, for each lamb.
Psalms 54:6For he has delivered me out of all trouble. My eye has seen triumph over my enemies.
Psalms 119:108My soul is continually in my hand, yet I won’t forget your law.