What is plasma?
Plasma is the fourth state of matter. It is an ionized gas, where the gas that has been energized to the point that some of the electrons break free from, but travel with, their nucleus - in other words allows both species of ions and electrons to coexist.
As far as we know, plasmas are the most common state of matter in the universe. Essentially, the sun, like most stars, is a great big ball of plasma. The sun's enormous heat rips electrons off the hydrogen and helium molecules that make up the sun.
They are even common here on earth. A spark in a gas will create a plasma. A hot gas passing through a big spark will turn the gas stream into a plasma that can be useful. Plasma torches like that are used in industry to cut metals.