Planck's law

(quantum mechanics) A fundamental law of quantum theory stating that energy associated with electromagnetic radiation is emitted or absorbed in discrete amounts which are proportional to the frequency of radiation.
(statistical mechanics) Planck radiation formula

The noun has one meaning:

Meaning #1: (physics) the basis of quantum theory; the energy of electromagnetic waves is contained in indivisible quanta that have to be radiated or absorbed as a whole; the magnitude is proportional to frequency where the constant of proportionality is give by Planck's constant