A filled space, or the concept of space as full of something.
1 a : a space or all space every part of which is full of matter b : an air-filled space in a structure; especially : one that receives air from a blower for distribution (as in a ventilation system)
2 : a general assembly of all members especially of a legislative body
3 : the quality or state of being full
Instead of thinking of the Universe as a vacuum dotted here and there with matter, consider it a plenum, a filled structure of space full of light, energy and particle/aniparticle pairs produced by the Zero Point Field fluctuation.