Mesons are incredibly small subatomic particles that are made of one quark and one antiquark. Antiquarks are the antimatter counterpart of a regular quark. Since antimatter quarks have the opposite spin of regular quarks, their spins can cancel each other out, which forms a particle similar to a Higgs Boson. The name meson comes from Greek "mesos", meaning middle. This is because the masses of the first mesons discovered were between the mass of light particles like electrons, called leptons, and heavy particles like protons, called baryons.