"Air molecules" refers to the tiny particles that make up the air we breathe. They are extremely small and constantly moving around us in the Earth's atmosphere. Full definition
A second detection system will make use of the faint glow caused by the collisions of shower particles with air molecules during cosmic ray air showers. (auger.org)
The rapid movement of an object (such as the speaker in my clock) throws surrounding air molecules into a frenzy. (discovermagazine.com)
The clay nanoparticles would spread out like sheets of paper scattered across a floor and keep air molecules from escaping, which kept the balls firm for an unusually long time. (discovermagazine.com)