The term spectral power distribution (SPD) means essentially the same thing as SED or spectral energy distribution (a distribution function of electromagnetic-radiation power distribution by wavelength or perhaps frequency) and is the preferred term in some non-astronomy fields such as descriptions of "everyday light" from natural sources and daylight. (It is perhaps the more logical term since an SED is indeed showing energy in terms of a rate rather than some total.) The term is rarely but occasionally used rather than SED in astronomy. See spectral energy distribution (SED) for the concept.
The initials SPD are also used in astronomy for other concepts, such as the spectral photon distribution, the distribution of photons sent or received per wavelength or frequency.