The term Spectral Power Distribution (SPD) indicates the function of Frequency (or Wavelength or photon energy) to power for an Electromagnetic Radiation (EMR) source (such as a star), transmitter, or sensor (such as a Spectrometer, this latter being called more specifically, its Sensitivity Function (S)). Typical illustration is a graph. The graph may be labeled Intensity versus frequency or wavelength, as intensity is defined in terms of power.
Sunyaev-Zel'dovich Effect (SZ Effect)
Vegetation Red Edge (VRE)