The measure of the force which air molecules push on a surface is called air pressure.

Here's a breakdown:

* Air pressure is the force exerted by the weight of air on a given area.

* Air molecules are constantly moving and colliding with each other and surfaces.

* These collisions create a force, and the total force exerted over a specific area is what we call air pressure.

You can also think of it as the weight of the air above a certain point. The higher you go, the less air is above you, and therefore the lower the air pressure.