noun. The ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.

noun. Specifically A physical constant by means of which the power of radiation of a body is quantitatively expressed.

noun. Emissive or radiating power.

noun. Tendency to emission; comparative facility of emission, or rate at which emission takes place

noun. The energy-emitting propensity of a surface, usually measured at a specific wavelength.

"The amount of blackbody energy emitted is strictly and solely a function of the thermal temperature of the substance, mitigated by the characteristic of the substance called emissivity (which can, as you say, by frequency dependent)."