MeV photons
we'll mention the photon equivalent to 1 million electron volts in what it says about light – but won't explain it here [note: although the crianca summary hints at this, the analogy itself isn't sufficient for an explicit explanation; we were looking for a more concrete one, like the nucleosynthesis term above]
Technical definition
Gamma-ray photons or other high-energy electromagnetic radiation with energies between 1 and 106 MeV.