A firmament; or, an extension, or a space or place extended or stretched out, and spread abroad like a tent or curtain, between the waters, though not exactly in the middle place; as Tyrus is said to sit, or be situated in the midst of the seas, Ezekiel 28:2, though it was but a little space within the sea. But of these things see more in Genesis 1:7.
Related Commentaries of Genesis 1:6
Genesis 1:6
6 And God said, Let there be a firmamentb in the midst of the waters, and let it divide the waters from the waters.