Albert Barnes Commentary Jeremiah 51:33

"For thus saith Jehovah of hosts, the God of Israel: The daughter of Babylon is like a threshing-floor at the time when it is trodden; yet a little while, and the time of harvest shall come for her." — Jeremiah 51:33 (ASV)

Translate, The daughter of Babylon is as a threshing-floor at the time when it is trampled, that is, trodden hard in readiness for the threshing: yet a little while and the harvest-time shall come to her, that is, overtake her. In the East, the grain, when reaped, is carried at once to the threshing-floor, a level spot carefully prepared beforehand, usually about 50 feet in diameter, and trampled hard. The grain, after it has been beaten out by a sledge drawn over it by oxen, is separated from the chaff and stored up in granaries.