The standard model of quarks and leptons is a united set of quantum mechanical theories encompassing electromagnetism, the weak force, which is responsible for beta decay, and the strong force, which holds atomic nuclei together. Before investigating the standard model, we need to describe the state of affairs previous to its development. The creation of high energy particle accelerators led to the discovery of a plethora of particles in addition to those already known. The electron, muon, and the electron and muon neutrinos are examples.
Hadrons are particles which interact via the strong force.
The proton and neutron are well known examples. The neutral lambda particle is another. Mesons are hadrons with integral spin, mainly 0 and 1. Examples are the pions and kaons. Strange particles are baryons and mesons which are unstable, but have much longer half-lives than other particles of similar mass and spin.