Physics a universal constant (h) which gives the ratio of a quantum of radiant energy (E) to the frequency (ν) of its source: it is expressed by the equation E = hν, and its approximate numerical value is 6.626 × 10 joule second
See Planck's constant in American Heritage Dictionary 4
noun Symbol h
The constant of proportionality relating the energy of a photon to the frequency of that photon. Its value is approximately 6.626 × 10-34 joule-seconds.