'Tent door' in the Bible

When he raised his eyes and looked up, behold, three men were standing [a little distance] from him. When he saw them, he ran from the tent door to meet them and bowed down [with his face] to the ground,

He said, “I will surely return to you at this time next year; and behold, Sarah your wife will have a son.” And Sarah was listening at the tent door, which was behind him.