The term for the pressure exerted by the weight of air in the atmosphere is atmospheric pressure. It is caused by the gravitational pull of the Earth on air molecules, which results in a force that can be measured using an instrument called a barometer. Atmospheric pressure varies with altitude, temperature, and local weather conditions. At sea level, it averages about 101.3 kPa or 760 mmHg. This pressure plays a crucial role in weather patterns, boiling points of liquids, and respiratory processes in living organisms.