Hadrons are subatomic particles made up of quarks, and they include protons, neutrons, and mesons. Other synonyms for hadrons include baryons, which are a type of hadron consisting of three quarks, and pions, which are a type of meson made up of a quark and antiquark. Additionally, kaons are also mesons consisting of a strange quark and either an up or down quark. Hadrons play a crucial role in particle physics, as they are involved in strong nuclear interactions. By studying hadrons, physicists can gain a deeper understanding of the fundamental nature of matter and energy in the universe.