Electromagnetic Radiation (EMR)'s Spectral Energy Distribution (SED) is a function, i.e., plot of brightness or Flux density versus the Frequency or Wavelength. When measured on Earth, the effects of Earth Atmosphere are relevant. A "complete" distribution often requires multiple instruments, leading to challenges in calibrating the data. A distribution over a limited bandwidth often provides signatures for specific types sources.
SED Fitting (aka Spectral Energy Distribution Fitting) is a method of classifying distant galaxies, to help determine their age and degree of Star Formation (SF). A challenge is that a young galaxy with Cosmic Dust has a SED across ultraviolet,page, Visible Light, and Near Infrared (NIR) as an old galaxy. A fitting method is Markov-Chain Monte Carlo (MCMC), using random walks around a parameter-space to determine the degree of unique fit between an SED and a known type of object. GalMC is an example of software that takes this approach.
Herschel Orion Protostar Survey (HOPS)
Spitzer Extended Deep Survey (SEDS)
Spectral Line Energy Distribution (SLED)
Stellar Model Atmosphere