So what is between planets? Between us and the Sun? Between the Inner, Outer, and Most Outer Areas of the Solar System? 

Interplanetary Medium.

What is that? Well, it's alot of stuff. For a long time, we thought this space was filled with NOTHING. But, we were wrong. 

The space is filled with something called "tennous gas". That means it is gas made of  neutral and ionized particles, along with small dust grains. 

It has an inner and outer boundary. The inner boundary (area) surrounding the sun and its corona. The outer boundary (area) called the Heliopause extending outward toward the planets. 

If time allows, and everyone is on task with all the other info we have to go over, we will circle back to this topic in more depth.