'Tent door' in the Bible

And the LORD appeared to him in the plains of Mamre: and he sat in the tent door in the heat of the day;

And he lifted up his eyes and looked, and lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground,

And he said, I will certainly return to thee according to the time of life; and lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.