Any of the subatomic particles that are built from quarks and thus interact via the strong force. The hadrons fall into two groups: mesons and baryons. Except for protons and neutrons, which are bound in nuclei, all hadrons have short lives and are produced in high-energy collision of subatomic particles. All hadrons are subject to gravitation; charged hadrons are subject to electromagnetic forces. Some hadrons break up by way of the weak force (as in radioactive decay); others decay via the strong and electromagnetic forces.