" Do you suppose it's a trap? Think they're waiting for us to penetrate the atmosphere and launch a ground attack?" " That seems a very poor tactic if it's so, but nevertheless, something's not right here." ― Jedi Generals Anakin Skywalker and Obi-Wan Kenobi
enters the atmosphere of Razor Crest Trask.
atmosphere was a collection of gases that surrounded a celestial body with sufficient mass, and therefore enough gravity to hold it. Examples included planets, moons, and large asteroids. Almost all species in the galaxy needed some form of atmosphere to breathe. Humans, as well as most other species, naturally breathed oxygen.
Most planets, like
Jakku, had a "Type I" atmosphere, to support most species. On worlds with a "Type II" atmosphere and above, oxygen-breathing species were advised to wear  breath masks.
 Moisture farms used vaporators to draw water from a planet's atmosphere.
Quarzite had a strong atmospheric pressure that was capable of crushing starships and flattening beings.