Naomi tells Ruth that that night Boaz will be winnowing barley at the threshing-floor. In this process grain was separated from the husks by being trodden out by animals. Then the mixture was thrown into the air against a stiff breeze, so that the wind blew the chaff away while the heavier grain fell more or less straight down. Threshing-floors were usually situated in exposed positions, so that they could catch the breeze (it was the measure of Gideon’s fear and desperation that he chose to beat out his wheat in a winepress, a most unsuitable location, Judg. 6:11).

She looks for Boaz to take action simply because she is who she is. She employs an expressive metaphor and asks him to spread his skirt over her. It is used similarly for taking in marriage in Ezekiel 16:8.