In Physics and Chemistry, plasma is an energetic state of atomic matter where some or all electrons in the outer orbitals have become separated from the atom. The result is a collection of ions and electrons which are no longer bound to each other. A plasma is sometimes called an ionized gas. The term plasma is generally reserved for a system of charged particles which is large enough to behave collectively (Debye shielding) so that a collection of a small number of charged particles are not usually called plasmas.
Three lower energy phases of matter are solid, liquid, and gas. Plasmas are the most common form of matter, comprising more than 99% of the visible universe. Everyday forms of plasma are the sun and stars, which are plasmas heated by nuclear fusion, fluorescent and neon lights, lightning, the Aurora borealis, solar wind, and interstellar nebulae
Sir William Crookes, an English physicist, identified a fourth state of matter, now called plasma, in 1879. The word 'plasma' was first applied to ionized gas by Dr. Irving Langmuir, an American chemist and physicist, in 1929.
See plasma physics for active research topics.
The word plasma has a greek root which means to be formed or molded (the word plastic shares this root) and has a few definitions: a green type of quartz (rare - first used in 1772); the fluid part of blood, lymph or milk (first used in 1845); an ionized gas (first used in 1928).