'Free will offering' in the Bible

And you shall keep the Feast of Weeks to Jehovah your God with a measure of a free-will offering of your hand, which you shall give according as Jehovah your God has blessed you.

That which has gone out of your lips you shall keep and perform, even a free-will offering, according as you have vowed to Jehovah your God, which you have promised with your mouth.