Plasma is often referred to as "the fourth state of matter," along with solid, liquid, and gas. It is an electrically quasineutral medium of unbound positive and negative particles, meaning that the overall charge of a plasma is roughly zero). Plasma is found in many places in the universe, including stars, lightning, and flames.

In addition to its presence in the universe, plasma is also found in the blood of living organisms. During the blood donation process, a special machine separates the plasma and often the platelets from the blood sample in a process called plasmapheresis. The remaining red blood cells and other blood components are then returned to the body, along with a little saline (salt) solution.

Plasma has unique properties that distinguish it from the other states of matter. For example, it can conduct electricity and respond to magnetic fields. Plasma is also used in many technological applications, such as in fluorescent lights, plasma TVs, and fusion reactors.