quantum field theory says that light is made of particles called photons, and, crudely speaking, the numbers constituting the electric and magnetic fields can be thought of as specifying how many photons there are at each time and place. Just as the strength of the electromagnetic field corresponds to the number of photons at each time and place, there are other fields corresponding to all the other elementary particles known. For example, the strengths of the electron field and the quark field relate to the numbers of electrons and quarks at each time and place.
