Plasma is an ionized gas- a gas into which sufficient energy is provided to free electrons from atoms or molecules and to allow both species, ions, and electrons, to coexist.
Plasma can be divided into hot and cold plasma. In hot plasma, electrons and ions have nearly the same energy (i.e., equal temperature), like the sun. Cold plasma is a non-equilibrium where the electron temperature is much hotter than the temperature of the ions and neutrals. Because cold plasma produces reactive species without burning the substrates, it has a wide array of applications in medical settings.