The plasmas of interest here are the electrically charged gases, or "ionized" gases, that are found in nature as well as in numerous devices. In addition to surrounding you in the universe, plasmas play key roles in bringing you sunlight outdoors during the daytime, street light at night, fluorescent light in your offices, computer chips in your computers, treated and coated surfaces of more important objects in your life than you might imagine (including hardened artificial joints you might have in your body and high temperature turbine blade coatings for the jets you fly in), flat panel displays for your TV, gas lasers, the welded joints that keep buildings from falling apart, and radio transmission around the world. Among the important applications expected in the future are the production of electrical energy from nuclear fusion, environmental cleanup, and space ship propulsion for interplanetary flights.
~ Gerald L. Rogoff, Coalition for Plasma Science
Plasma is often called the "Fourth State of Matter," the other three being solid, liquid and gas. A plasma is a distinct state of matter containing a significant number of electrically charged particles, a number sufficient to affect its electrical properties and behavior. In addition to being important in many aspects of our daily lives, plasmas are estimated to constitute more than 99 percent of the visible universe.