Baryons are what atoms, and therefore everything made of atoms, are built out of.
Baryons belong to the hadron family, meaning they are composite particles made of quarks. More specifically, they are a type of hadron that consists of 3 quarks bound together by the strong nuclear force, mediated by gluons. The most familiar baryons are the proton and neutron, which make up atomic nuclei and form the foundation of all matter. There are plenty of more exotic ones too, like the Lambda (Λ), Sigma (Σ), Xi (Ξ) and Omega (Ω) baryons, which contain heavier quarks and are often found in high-energy particle collisions or inside neutron stars.
The quark composition is what distinguishes them. While protons and neutrons are built from “up” and “down” quarks (the lightest and most stable types), other baryons can include strange, charm, bottom or even top quarks, making them much heavier and more unstable. These exotic baryons decay quickly into lighter particles, which is why we don’t see them in everyday life, but they play a huge role in particle physics experiments and extreme environments.
Baryons also follow the Pauli exclusion principle, which means no two identical baryons can occupy the same quantum state. This is why neutron stars, made almost entirely of neutrons, resist collapsing despite their immense gravity, quantum mechanics literally holds them up!
Baryons dominate the visible universe, but most of the mass in the cosmos is not baryonic. Dark matter, whatever it is, doesn’t seem to be made of baryons at all. So protons and neutrons form everything we can see, planets and stars and life included, and something invisible outweighs them anyway.