When two or more quarks are held together by the strong nuclear force, the particle formed is called a hadron. Quarks that make the quantum number of hadrons are named 'valence quarks'. The two families of hadrons are baryons (made of three valence quarks) and mesons (which are made from a quark and an antiquark). Some examples of baryons are protons and nuetrons, and examples of mesons are pions and kaons.