What is a plasma?
Plasma is one of the four fundamental states of matter (the others, as you may know, are solid, liquid, and gas).
When air or gas is ionized, plasma forms with similar conductive properties to that of metals. Plasma is the most abundant form of matter in the Universe, because most stars are in plasma state.
Plasma is loosely described as an electrically neutral medium of positive and negative particles. It is important to note that although they are unbound, these particles are not ‘free’. When the charges move they generate electrical currents with magnetic fields, and as a result, they are affected by each other’s fields.
Plasmas are by far the most common phase of ordinary matter in the universe, both by mass and by volume. Our Sun, and all stars, are made of plasma, much of interstellar space is filled with a plasma, albeit a very sparse one, and intergalactic space too.