The word plenum gets tossed around a lot when talks of audio video arise, but what does it really mean? Plenum is a space, typically above a ceiling or below a floor that serves as a chamber for cooled or heated air at inhabited places. Examples are air conditioning, heating and ventilation systems. When integrating cables in these types of spaces, a plenum-rated cable is necessary to avoid or contain possible hazards associated with a fire. Plenum cables are coated with Teflon or any other type of fire-retardant to deflect hazards such as toxic gasses and smoke as it burns. HDMI, twisted pair, coaxial, VGA, DVI and other AV cables are now made in plenum versions.