A neutrino is a subatomic particle with a mass much smaller than other known subatomic particles. For scale, if a single atom was the size of the solar system a neutrino would be the approximate size of a walnut. Billions of neutrinos pass through your body every second, many originating from the sun as solar neutrinos.
Every Nemosine Neutrino pen box is marked with the proton:proton reaction
that generates neutrinos in the Sun through nuclear fusion, when:
2 protons --> deuterium + positron + electron neutrino