1. The layer of gas surrounding a planet or other celestial body: This is the most common meaning of "atmosphere." It's what we breathe, protects us from harmful radiation, and helps regulate our planet's temperature. Earth's atmosphere is made up of nitrogen, oxygen, carbon dioxide, and other gases.
2. The general mood or feeling of a place or situation: This is a more figurative meaning. For example:
* "There was a tense atmosphere in the room as they waited for the verdict."
* "The restaurant had a cozy and romantic atmosphere."
3. A specific type of musical or artistic style: This meaning is less common but is used to describe a particular creative approach or trend.
* "The band's music has an experimental atmosphere."
4. In the context of pressure: This is related to the first meaning. "Atmospheric pressure" refers to the weight of the air pressing down on us at a given location.
Let me know if you'd like a more in-depth explanation of any of these meanings, or if you had a specific usage in mind.