composite particle made up of an odd number of elementary particles.
The most important examples by far are the proton and the neutron.
"Barys" means "heavy" in Greek, because protons and neutrons was what made most of the mass of known ordinary matter, as opposed notably to electrons.
Baryons can be contrasted with:
  • mesons, which have an even number of elementary particles. The name meson comes from "medium" since their most common examples have two quarks rather than three as the most common baryons such as protons. So they have less mass than a proton, but more than an electron, this medium mass.
  • leptons, which are much lighter particles such as the electron. "Leptos" means "fine, small, thin".