In Biblical cosmology, the firmament is the structure above the atmosphere, conceived as a vast solid dome. According to the Genesis creation narrative, God created the firmament to separate the "waters above" the earth from the "waters below" the earth. The word is anglicized from Latin firmamentum, which appears in the Vulgate, a late fourth-century Latin translation of the Bible.

Answer this question: what is the definition of firmament in the bible? Let's think fast. Stream of consciousness:
The important part for answering this question is: In Biblical cosmology, the firmament is the structure above the atmosphere, conceived as a vast solid dome. So the final answer is the structure above the atmosphere , conceived as a vast solid dome.