A power law in statistics is a relationship between quantities where one is proportional to the power of the other. Often such relations only hold over a given range. Template (for quantities x and y):
Subtypes include "square law" and "inverse-square law". Some physics examples:
A power law spectrum is an EMR spectrum such that the flux at each frequency is related to that frequency by a power law, the exponent being referred to as its spectral index. Such a spectrum can only fit this description over a particular regime, lest it reach infinities. Synchrotron radiation is described as such a power law spectrum. The black-body spectrum is not, peaking in the center, but its longer-wavelength portion is usefully treated as a power law spectrum. Cosmic rays' spectrum is basically power law.