Plasma (physics)
Plasma is created by adding energy to a gas so that some of its electrons leave their atoms. This is ionization. It results in negatively charged electrons, and positively charged ions. Unlike the other states of matter, the charged particles in a plasma react strongly to electric and magnetic fields (i.e. electromagnetic fields). If a plasma loses heat, the ions will re-form into a gas, emitting the energy which had caused them to ionize.