What is "asman"

Asman is the Avestan and Middle Persian name of the Zoroastrian divinity that is the hypostasis of the sky. Asman is the "highest heaven," and is distinguished from the firmament (thwasha), which lies nearer the earth. The 27th day of the Zoroastrian calendar is dedicated to him.

In the Avesta, specifically in the Vendidad, the word is mentioned as being the first thing created. The word is also the origination of the word asman in modern Persian and Pashto.