The Planck constant, or Planck's constant, is the quantum of electromagnetic action that relates a photon's energy to its frequency. The Planck constant multiplied by a photon's frequency is equal to a photon's energy. The Planck constant is a fundamental physical constant denoted as ${\displaystyle h}$, and of fundamental importance in quantum mechanics. In metrology it is used to define the kilogram in SI units.^[2]

The Planck constant is defined to have the exact value ${\displaystyle h=}$ 6.62607015×10⁻³⁴ J⋅s in SI units.^[3][4]

At the end of the 19th century, accurate measurements of the spectrum of black body radiation existed, but predictions of the frequency distribution of the radiation by then-existing theories diverged significantly at higher frequencies. In 1900, Max Planck derived empirically a formula for the observed spectrum. He assumed that a hypothetical electrically charged oscillator in a cavity that contained black-body radiation could only change its energy in a minimal increment, ${\displaystyle E}$, that was proportional to the frequency of its associated electromagnetic wave.^[5] He was able to calculate the proportionality constant, ${\displaystyle h}$, from the experimental measurements, and that constant is named in his honor. In 1905, the value ${\displaystyle E}$ was associated by Albert Einstein with a "quantum" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle. It was eventually called a photon. Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta".

Since energy and mass are equivalent, the Planck constant also relates mass to frequency. Wiki

Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation and eventually build a structure which has no relation to reality. - Tesla

It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. -Feynman

All these fifty years of conscious brooding have brought me no nearer to the answer to the question, “What are light quanta?” Nowadays every Tom, Dick, and Harry thinks he knows it, but he is mistaken. - Einstein 1954

Anything quantum is BS. Scientists today still don't understand what exactly is light/EM wave/quantum/energy/photon.

Energy/light/EM wave must coexist with the matter/medium/carrier. There is no light in the vacuum space.

Light is alternating current in the medium/air/water/matter. Visible light oscillating at the visible frequency. 

All atoms/matters are AC generator, transformer, perpetual machine.

All matters in space are connected/coexisting by two forces, universal gravitation force and universal repulsion force/levity in physics. All matters are entangled by forces, simultaneously motion forever.