the.com/air pressure

means The force exerted by the weight of air pressing on a surface, measured as pounds per square inch or in units like pascals and millibars.

from 'Pressure' traces back to Latin pressura, from premere 'to press,' the same root behind 'print' and 'compress.' The concept of air having weight at all is a 1600s discovery — Torricelli's mercury barometer and the famous Magdeburg hemispheres experiment (where teams of horses couldn't pull apart two bowls held together by nothing but a vacuum) proved the invisible sky was quietly, massively pushing on everything all along.