A gas heated until its atoms lose electrons and become ionized becomes plasma.
Plasma is commonly called the fourth state of matter, following solid, liquid, and gas. Heating supplies enough energy for collisions to remove electrons from atoms, producing a mixture of positively charged ions and free electrons. Plasma can also form through powerful electric fields or other forms of energy input, and it does not need to be completely ionized.
Unlike an ordinary neutral gas, plasma conducts electricity and responds strongly to electric and magnetic fields. Its charged particles can behave collectively, creating phenomena such as currents, waves, and magnetic structures. Overall, a plasma is often electrically quasineutral even though it contains many charged particles.
Plasma is common throughout the universe: stars, including the Sun, are made largely of it, and much interstellar matter is plasma. On Earth, examples include lightning, the glowing gas in neon signs, electric arcs, and some industrial cutting and etching systems. A common misconception is that every extremely hot gas is automatically plasma; the key distinction is significant ionization and collective electromagnetic behavior.