Plasma is a gas that is so hot that the molecules or atoms lose some of their electrons. On Earth, the most common forms of matter are solid, liquid, and gas. But in the universe as a whole, the most common form of matter is a plasma.
The sun is a big ball of plasma. Lightning is a plasma. The electric sparks you get from static electricity are made of plasma. There is a plasma inside every glowing fluorescent light tube and every neon light.
Plasmas consist of electrons and the positively charged atoms the electrons were stripped from. These atoms that are missing electrons are called ions, and we say that the gas that has become a plasma has been ionized. Gases that have only a small percentage of their atoms stripped of electrons are said to be weakly ionized. When more of the atoms are affected, we say the plasma is highly ionized.
Most flames are weakly ionized plasmas. Sparks and lightning can be highly ionized.
Because electrons carry a negative charge, and stripped atoms carry a positive charge, plasmas can conduct electricity. Gases do not conduct electricity.
Plasmas can emit colors just like flames do. The color of a neon light is due to excited electrons emitting light to lose energy and fall back into their normal energy levels. Other plasmas emit other colors, since their atoms or molecules have different energy levels. Helium plasmas are pink. Plasmas made from sodium vapor are the characteristic yellow of sodium.