Atmospheric pressure, or air pressure, is the force per unit area exerted by the weight of air in the atmosphere of Earth. It is measured with a barometer, and is most commonly expressed in units of hectopascals (hPa).
Atmospheric pressure can vary significantly depending on factors such as latitude, altitude, weather conditions, and season. Generally, pressure decreases as altitude increases, and pressure increases as latitude decreases. Pressure is also higher in warmer weather and during the summer than it is in colder weather and during the winter. Additionally, atmospheric pressure can be affected by changes in air circulation and air mass, such as during storms.