What is Plasma? Plasma is the fourth state of matter. It differs from solids, liquids and gases in so far as it's atoms are divided into free-floating 'negative' electrons and 'positive' ions (an atom which has lost its electron/s). It is sometimes referred to as an ionized gas. Students are generally taught about only three states of matter, and when Plasma does get a mention, little importance is assigned. Not only should plasma be added to the list, but the order should be reversed to put it in first place. The reasons for this will become clear. The term Plasma was borrowed from blood plasma in order to describe its almost life-like and self-organising properties. Plasma sometimes emits light when under the excitation of electrical and magnetic fields. Polar auroras bear witness to this fact.