Baryons are massive particles which are made up of three quarks in the standard model. This class of particles includes the proton and neutron. Other baryons are the lambda, sigma, xi, and omega particles. Baryons are distinct from mesons in that mesons are composed of only two quarks. Baryons and mesons are included in the overall class known as hadrons, the particles which interact by the strong force. Baryons are fermions, while the mesons are bosons. Besides charge and spin (1/2 for the baryons), two other quantum numbers are assigned to these particles: baryon number (B=1) and strangeness (S), which in the chart can be seen to be equal to -1 times the number of strange quarks included. 
The conservation of baryon number is an important rule for interactions and decays of baryons. No known interactions violate conservation of baryon number.Recent experimental evidence shows the existence of five-quark combinations which are being called pentaquarks. The pentaquark would be included in the classification of baryons, albeit an "exotic" one. The pentaquark is composed of four quarks and an antiquark, like a combination of an ordinary baryon plus a meson.
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