A baryon is one of the two types of hadrons, the other being the meson (particle). In 1964 Murray Gell-Mann and George Zweig independantly theorized that hadrons are made of quarks. Modern research has found that a baryon is composed of three quarks or three anti-quarks (making an anti-baryon). There are 120 types of baryon. Examples: proton, anti-proton, lambda, neutron, omega...