antiparticle a particle that has the same mass as another particle but has opposite values for its other properties; interaction of a particle and its antiparticle results in annihilation and the production of radiant energy
hadron any elementary particle that interacts strongly with other particles
lepton an elementary particle that participates in weak interactions; has a baryon number of 0
quark (physics) hypothetical truly fundamental particle in mesons and baryons; there are supposed to be six flavors of quarks (and their antiquarks), which come in pairs; each has an electric charge of +2/3 or -1/3; "quarks have not been observed directly but theoretical predictions based on their existence have been confirmed experimentally"