||Ple"num, n. (Ventilation) A condition, as in an occupied room, in which the pressure of the air is greater than that of the outside atmosphere; as, a plenum may exist in a hall ventilated by a fan blower.

||Ple"num (?), n. [L., fr. plenus full.] That state in which every part of space is supposed to be full of matter; -- opposed to vacuum. G. Francis.

||Ple"num, n. (Ventilation) A condition, as in an occupied room, in which the pressure of the air is greater than that of the outside atmosphere; as, a plenum may exist in a hall ventilated by a fan blower.

• A legislative meeting in which all members are present
  
• A space that is completely filled with matter
  
• An enclosed space having greater than atmospheric pressure
  
• The space above a false ceiling used for cables, ducts etc
  
• (computing) A type of network cabling which satisfies plenum-ratings issued by the National Electrical Code. These cables are safer in case of a fire, producing less smoke and fumes.