An subatomic particle is a particle that is smaller than an atom. Subatomic particles include protons, neutrons, electrons, photons, and quarks. Other particles that could be included in this category depending on the definition of subatomic particle include mesons, bosons and gravitons. Protons and neutrons are located in the nucleus of an atom, while electrons orbit around the nucleus. Photons are particles of light, while quarks are the fundamental building blocks of protons and neutrons.