This report summarizes the physics results presented as part of the
cosmic-ray indirect (CRI) session of the $37^{\rm th}$ICRC conference.
Updated measurements on cosmic-ray energy spectrum, mass composition,
and arrival direction distributions were presented by several
collaborations, spanning the energy range of a few TeV up to the highest
observed energies. We select some of the results which were highlighted
by the respective discussion leaders or which presented new results at
this conference. Results on atmospheric phenomena, including TGFs and
thunderstorms are also presented.
We see a few interesting trends in the presented data. Among these are,
the increased use of IACT's to study cosmic-rays among experiments primarily
intended for gamma-ray measurements. Another, is the continued development
of radio detection of air showers. Multi-component detectors are becoming
the preferred detection mode, as the knowledge of how to integrate the
different information about an air shower collected by the different detector
components improves.
The main physics questions about the origins of cosmic rays, both galactic
and extra-galactic, remain open. Increased statistics and improved analyses
allow for refining and better constraining theoretical models, but no
definitive answers can be claimed thus far. Looking forward, the field is
moving at a rapid pace; Several detectors upgrades are underway, data is
continually coming in and analyzed, old data being made public for a wider
audience and a new generation of scientists to examine, with new tools and
approaches that will hopefully result in new insights to help solve the
open questions on cosmic-rays.