'Free will offerings' in the Bible

And there you shall bring your burnt offerings, and your sacrifices, and your tithes, and heave offering of your hand, and your vows, and your free-will offerings, and the first-born of your herds and of your flocks.

You may not eat inside your gates the tithe of your grain or of your wine or of your oil, or the first-born of your herds or of your flock, or any of your vows which you vow, or your free-will offerings or the heave offering of your hand.