1. The envelope of gases surrounding the Earth and other celestial bodies which is held by the force of gravity: The atmosphere of the Earth is being affected by pollution caused by the increased exploitation of natural resources.

The atmosphere consists of four distinct layers whose boundaries are not precise:

• The "troposphere" (extending from sea level to about 5-10 miles [10 to 20 km] above the earth.
• The "stratosphere" (up to about 30 miles [50 km]).
• The "mesosphere" (up to about 60 miles [96 km]).
• The "thermosphere" (up to about 300 miles or more [480 km]).

The upper region of the troposphere is often regarded as a separate region known as the "exosphere".

2. The gas bound gravitationally to a planet or the pressure of the air on the Earth at mean sea level approximately 14.7 pounds per square inch or 760 millimeters high at 0 degrees Celsius under standard gravity: Through the powerful telescope, the astronomers were able to study the atmosphere of the distant planets.

Although some details about the atmospheres of other planets and satellites are known, only the Earth's atmosphere has been well studied, the science of which is called "meteorology".

3. The outer layers of a star: The atmosphere surrounding the star appears to cause the twinkle effect which romantic couples dream about.
4. A supposed outer envelope of effective influences surrounding various bodies: The atmosphere of the capital city was one of individuals and corporations attempting to influence politicians.
5. Prevailing psychological climate; a pervading tone or mood; a characteristic mental or moral environment; a fascinating or beguiling association or effect: The atmosphere in the office appeared to be edgy as if there were major staff changes anticipated, but no one knew when that would happen.
6. Applied to the background sounds that evoke a particular mood, impression, setting, etc., in a broadcast program, etc.: The atmosphere created by the music was dark and mysterious.
7. The air in any particular place, especially as affected in its condition by heat, cold, purifying or contaminating influences, etc.: The old wood stove was not well maintained and smoked, creating a smoky atmosphere in the cabin.
8. The predominant tone or mood of a work of art, or the pervading quality, effect, or mood, especially as associated with a particular place: Henry lived in a dark old house with a depressing atmosphere.
9. A distinctively exotic or romantic quality or effect: Willy and Gertrude went to an Italian restaurant where there was lots of atmosphere.

In geology, The air occupying the pore or open spaces in soil: Soil atmosphere can be a gas located in the pores or cavities in the soil or, in other words, in the zone of aeration.