'Free will offerings' in the Bible

Speak to Aaron and to his sons and to all the sons of Israel, and say to them: Any man of the house of Israel, or of the strangers in Israel, who offers his sacrifices for his vows, for all his free-will offerings, which they will offer to Jehovah for a burnt offering,

besides the sabbath of Jehovah, and besides your gifts, and besides all your vows, and besides all your free-will offerings which you give to Jehovah.