Answer: plenums

AnswerCrossword Clue
PLENUMSFall assemblies.
plenumsPLENUM, space considered as fully occupied by matter
plenumsA space completely filled with matter, or the whole of space so regarded
plenumsAn enclosed chamber where a treated substance collects for distribution, as heated or conditioned air through a ventilation system
plenumsAn assembly of all the members of a group or committee