Plasma is known as the fourth state of matter (the first three states being solid, liquid and gas).
Matter in ordinary conditions on Earth has electrons that orbit around the atomic nucleus. The electrons are bound to the nucleus by the mutual, electrostatic attractive force. If the temperature is high enough, the electrons (at least those of the outermost orbits) acquire enough kinetic energy to escape the atom’s potential (similar to a spacecraft that escapes the Earth’s gravitational pull). In this situation the electrons are no longer trapped in orbits around the nucleus. This is the plasma state, where a gas becomes a collection of negatively charged electrons which have escaped the pull of the nucleus and ions which are positively charged because they have lost one or more electrons.
The majority of the matter in the universe is actually found in the plasma state. This is because stars are made up of material in the plasma state.
source: windows to the universe