Albert Barnes Commentary Ruth 3:4

"And it shall be, when he lieth down, that thou shalt mark the place where he shall lie, and thou shalt go in, and uncover his feet, and lay thee down; and he will tell thee what thou shalt do." — Ruth 3:4 (ASV)

Uncover his feet - Rather, “the place of his feet;” the foot of his bed, as we should say. So also (Ruth 3:7–8).