'Freewill Offering' in the Bible

and at his side, Amasiah the son of Zicri, who had made a freewill offering to Yahweh, and with him [were] two hundred thousand mighty armed warriors.

And Kore the son of Imnah the Levite, the porter toward the east, was over the freewill offerings of God, to distribute the oblations of the LORD, and the most holy things.

His officers also contributed a voluntary offering to the people, the priests and the Levites. Hilkiah, Zechariah, and Jehiel, the officials of the house of God, gave to the priests for the Passover offerings 2,600 from the flocks [of lambs and young goats], and 300 bulls.