Definitions for "Air shower"
Cascades of particles produced when highly energetic cosmic rays collide with atoms and molecules in Earth's upper atmosphere.
a cascade of particles caused by the interaction of a high-energy gamma-ray (also occurs with cosmic rays) with the atmosphere; the gamma-ray interacts to produce an electron/positron pair, this pair then interacts with the atmosphere to produce more particles, and so on until the shower reaches the Earth, at which time millions of particles have been produced as a result of that one incoming gamma-ray
See cascade shower.