'Free will offering' in the Bible

then ye have prepared a fire-offering to Jehovah, a burnt-offering, or a sacrifice, at separating a vow or free-will-offering, or in your appointed things, to make a sweet fragrance to Jehovah, out of the herd, or out of the flock.

The produce of thy lips thou dost keep, and hast done it, as thou hast vowed to Jehovah thy God; a free-will-offering, which thou hast spoken with thy mouth.

With a free will-offering I sacrifice to Thee, I thank Thy name, O Jehovah, for it is good,