Emissivity

The ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area; expressed as a number between 0 and 1.

The ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area.

The fractional amount of radiation emitted by a given object or substance in comparison to the amount emitted by a perfect emitter.

The ratio of power radiated by a substance to the power radiated by a blackbody at the same temperature.