The fundamental particle that carries the strong nuclear force is the gluon. Gluons are massless gauge bosons that mediate the strong interaction between quarks, binding quarks together inside particles such as protons and neutrons.
The strong interaction is described by quantum chromodynamics, or QCD. Quarks possess a property called color charge, and gluons transfer color charge as they are emitted and absorbed. Unlike photons, which carry no electric charge, gluons themselves carry color charge. That allows gluons to interact with one another, making QCD mathematically richer than electromagnetism.
There are eight independent types, or color states, of gluon. Their behavior helps explain both confinement—the fact that isolated quarks are not observed—and asymptotic freedom, in which quarks interact more weakly at extremely short distances. Gluons are sometimes confused with mesons. Gluons carry the fundamental strong interaction between quarks, while mesons can mediate the residual strong force between composite particles such as protons and neutrons. The photon carries electromagnetism; W and Z bosons carry the weak interaction.