Definition of "emissivity" [em•is•siv•i•ty]

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "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)."
• "Buy double-or triple-pane models, designated Energy Star with a "low E" (for "emissivity") coating."
• "Perhaps the most interesting realization is that the concept of reciprocity applies to the ‘kludge’ factor called emissivity – the correction value that permits a greybody to be modeled with planck’s law and stefan’s law – applies to the atmosphere."