'Threshing' in the Bible

Now Ornan was threshing wheat, and he turned back and saw the angel; and his four sons who were with him hid themselves.

Ornan said to David, “Take it for yourself; and let my lord the king do what is good in his eyes. See, I will give you the oxen also for burnt offerings and the threshing sledges (heavy wooden platforms) for wood and the wheat for the grain offering; I give it all.”