What is a plasma?
An ionized gas made up of electrons, ions and neutral particles, but electrically neutral.
The word was first used by Irving Langmuir in 1928 to describe the ionized gas in an electric discharge.
Fourth state of matter. Consider the series of phase transitions solid-liquid-gas. If we continue to increase the temperature above, say, 20 000 K (lower if there is a mechanism for ionizing the gas) we obtain a plasma.