Planck's constant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics the constant of proportionality (symbol h), relating the energy and frequency of a photon (6.626 x 10-34 joule-seconds); also related to the indeterminacy limit in the Heisenberg uncertainty principle; the quantum of action

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second