The pressure exerted by the atmosphere; air pressure (as measured in weather reports, etc.).
今日は気圧が低いので頭が重い気がする。
Because the atmospheric pressure is low today, I feel a heaviness in my head.
台風の接近で気圧が急激に下がった。
The atmospheric pressure dropped rapidly as the typhoon approached.
高山では気圧が低くなるため、体調に注意が必要だ。
At high altitudes the air pressure decreases, so you need to pay attention to your physical condition.
The unit of pressure called the atmosphere (atm), used in physics and engineering.
標準大気圧は約1気圧（1 atm）で表される。
Standard atmospheric pressure is expressed as about 1 atmosphere (1 atm).
この実験は真空中で0.01気圧まで減圧した状態で行った。
This experiment was carried out in a reduced pressure condition down to 0.01 atm.