A hadron is a subatomic composite particle made of two or more quarks held together by the strong force. All known hadrons are made of either two or three quarks:
Two of the most common particles in the Universe are hadrons: the proton and the neutron, both baryons. The join together to make up atomic nuclei which, when combined with electrons (which are leptons), create atoms. As such, hadrons and specifically baryons are the building blocks of all matter.