A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of electromagnetic or mechanical radiation, most commonly light. It is used in many branches of astronomy to characterize astronomical sources. Features of the SED found in specific regions of the electromagnetic spectrum, such as absorption or emission lines, provide information about the object being studied. For example, in radio astronomy they are used to show the emission from synchrotron radiation, free-free emission and other emission mechanisms. In infrared astronomy, SEDs can be used to investigate young stellar objects, galaxies at high redshift, and objects heavily obscured by dust.