ELI5: Explain Like I'm 5

Interstellar medium

The interstellar medium is like the air we breathe but in space. It’s the space between stars and around galaxies. The interstellar medium is made of very small pieces of gas and dust. It’s not always the same because it can change over time. The gas and dust can move from place to place and some stars form from them. Without the interstellar medium, it would be hard for stars to form like our Sun.