Too Other
All that is seemingly not present — though somehow active — does not exist as distinct things. It is somewhere in between, between the things. It is the space between, its substance. It is that what makes up space.
As such it is ungraspable — unless it does become something, a thing. So many things may emerge out of space. At last, space is totally made of things, nothing else. They just cannot be seen — in the moment. Maybe they are too small, too big, too far away, too close, too well-known, too strange, too many …
Still, somehow they are there, and they have some influence on those things that can be seen. So we give them a name, as a whole. Here, in this context, we call it “space”. (But we must not forget that it is what we call “knowledge”, too. And “activity”. And, of course, “thing”s.)