'Tent door' in the Bible

Now the Lord appeared to him by the oaks of Mamre, while he was sitting at the tent door in the heat of the day.

When he lifted up his eyes and looked, behold, three men were standing opposite him; and when he saw them, he ran from the tent door to meet them and bowed himself to the earth,

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.