'Grain floor' in the Bible

And now, is there not Boaz, our relation, with whose young women you were? See, tonight he is separating the grain from the waste in his grain-floor.

So take a bath, and, after rubbing your body with sweet oil, put on your best robe, and go down to the grain-floor; but do not let him see you till he has come to the end of his meal.

And she went down to the grain floor and did according to all that her mother-in-law had told her.

And she took her rest at his feet till the morning: and she got up before it was light enough for one to see another. And he said, Let it not come to anyone's knowledge that the woman came to the grain-floor.