Final answer:
The property being referred to with two parallel plates of infinite dimensions with emissivities is the Stefan-Boltzmann law, which relates to the total power emitted per unit area from a blackbody.
Step-by-step explanation:
The question 'For two parallel plates of infinite dimensions with emissivities, what property is being referred to?' pertains to the subject of thermal radiation in the context of blackbody radiation. The property being referred to in the question is most likely the Stefan-Boltzmann law, which describes the total power emitted per unit area of a blackbody and is proportional to the fourth power of the blackbody's temperature (T). This law is mathematically expressed as P = σAeT4, where σ is the Stefan-Boltzmann constant (~5.67 x 10-8 W/m2/K4), A is the surface area, and e is the emissivity of the plates. The Stefan-Boltzmann law can be derived using integral calculus on Planck's blackbody radiation law over all wavelengths.