ISM

 

Interstellar space: What is it and where does it begin?

"Interstellar space is the area between the stars, but it is far from empty. It contains vast quantities of neutrinos, charged particles, atoms, molecules, dark matter and photons ranging from the highest-energy radiation to the sluggish light of the cosmic microwave background (CMB) albeit rather sparsely spread out."

Its not:

"NOTHING"

as some would have you believe.

Space itself would be something let alone all the:

neutrinos, 

charged particles, 

atoms, 

molecules, 

dark matter 

and photons ranging from the highest-energy radiation 

to the sluggish light of the cosmic microwave background

etc.