'Free will offerings' in the Bible

Speak unto Aaron, and to his sons, and unto all the children of Israel, and say unto them, Whosoever he be of the house of Israel, or of the sojourners in Israel, that offereth his oblation, whether it be any of their vows, or any of their freewill-offerings, which they offer unto Jehovah for a burnt-offering;

besides the sabbaths o Jehovah, and besides your gifts, and besides all your vows, and besides all your freewill-offerings, which ye give unto Jehovah.