In particle physics, mesons are subatomic particles composed of one quark and one antiquark. They are part of the hadron particle family—particles made of quarks. The other members of the hadron family are the baryons—subatomic particles composed of three quarks.
The main difference between mesons and baryons is that mesons are bosons while baryons are fermions—that is, mesons have integer spin while baryons have half-integer spin—meaning that the Pauli exclusion principle does not apply to mesons.
Each meson has a corresponding antiparticle (antimeson) where quarks are replaced by their corresponding antiquarks and vice-versa.