This entry contributed by Riku Jarvinen
A plasma is an ionized and macroscopically neutral gas with sufficient amount of free charges to make electromagnetic forces important to its macroscopic behavior. It is sometimes called the fourth state of matter.
Electron, Gas, Ion, Plasma Frequency, Plasma Physics
References
Correll, D. "Plasma Dictionary." http://plasmadictionary.llnl.gov/.
Griem, H. R. Principles of Plasma Spectroscopy. New York: Cambridge University Press, 1998.
