You are most likely familiar with the solid, liquid and gaseous states of matter. Usually a solid that is heated will turn into a liquid which if heated further will turn into a gas. You know that if solid ice is heated it will become liquid water which if boiled will become gaseous water vapor.
However, you may not be familiar with what is called the fourth state of matter. This state of matter exists heavily in space.
The upper atmosphere of Earth and all of the other planets, as well as the rest of the solar system is filled with this fourth state of matter. It is called plasma. I bet you have heard of plasma TV's.
Plasma is actually the most common form of matter in the universe!