In purely classical Maxwell theory the electromagnetic energy transmission is described by the Poynting vector defined as
#S=E\timesH#
where #E# is the electric field vector and #H# is the magnetic field vector and the product is a cross product, so S is also a vector.
The physical meaning of #S# is that its norm represents the energy per unit of area in the point where it is evaluated, and its direction is where that energy will move.
Because both #E# and #H# can oscillate with time as waves, the Poynting vector can have an amplitude that oscillate and propagate in time following as direction the direction of motion of the electromagnetic wave.
In quantum electrodynamics, the energy of the field is transported by photons where each photon carries an energy of #h\nu# with #h# the Plank constant and #\nu# the frequency.
