What does baryon mean?
A baryon is a subatomic particle built from three quarks held together by the strong nuclear force. Protons and neutrons — the particles that make up atomic nuclei — are the best-known examples, meaning nearly all ordinary, visible matter in the universe is baryonic. Baryons belong to the broader family of hadrons, distinguished from mesons (which contain only a quark–antiquark pair) by their three-quark structure, and they carry half-integer spin, making them fermions. Each baryon also carries a conserved quantum property called baryon number. The word appears mainly in particle physics and cosmology: researchers speak of baryon density, baryon asymmetry (the puzzling excess of matter over antimatter), and searches for exotic baryons containing heavier quarks. Though strictly a specialist term, it underpins some of the biggest questions in science — why anything material exists at all — since without baryons there would be no atoms, no stars, and no people.
nounA baryon is a subatomic particle made of three quarks bound together by the strong force, such as a proton or neutron. Baryons are the heavy class of hadrons and account for most of the visible matter in the universe.
- A subatomic particle composed of three quarks bound by the strong force, including protons and neutrons; the heavy class of hadrons.
"Protons and neutrons, the building blocks of atomic nuclei, are the two most familiar baryons."
"Physicists at the collider identified a previously unobserved exotic baryon containing four quarks' worth of charge configurations."
"Because baryon number is conserved in the Standard Model, the universe's surplus of matter over antimatter remains one of physics' deepest puzzles."
Regular plural; countable. Often used with adjectives such as 'exotic', 'heavy', or 'strange' when discussing particle species.
"The Standard Model predicts many more baryons than have yet been observed experimentally."
Every proton in your body is a baryon — which means you are, quite literally, mostly made of them.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of baryon
The word 'baryon' derives from the Greek 'barys', meaning 'heavy', chosen because baryons are heavier than leptons and mesons. It was coined in the mid-twentieth century, during the period when physicists were systematically classifying the growing zoo of subatomic particles. The same Greek root gives English several other scientific terms, including 'barium' (the heavy element), 'baritone' (literally 'deep-sounding'), and 'barycenter' (the center of mass around which bodies orbit).
Related word forms
How baryon is actually used
A technical term used almost exclusively in particle physics, cosmology, and related scientific writing; rare in everyday speech. In casual contexts, speakers usually name specific baryons (proton, neutron) rather than using the general term. The adjective form 'baryonic' appears frequently in cosmology, as in 'baryonic matter'.
Easily confused with baryon
A meson is a hadron composed of one quark and one antiquark, whereas a baryon is made of three quarks.
A lepton (such as an electron) is an elementary particle that does not feel the strong force, while a baryon is a composite particle of quarks held together by it.