In physics, plasma is the fourth state of matter. All ‘stuff’ in the universe is made of matter, but we are only familiar with it being a solid, liquid or gas. Heating any gas to a high enough temperature will cause the electrons in atoms to be stripped away from their associated nuclei, leaving just protons and neutrons.
These protons and neutrons are called ions and are positively charged due to the lack of negative electrons. Clouds of ions or electrons are known as plasma and only occur at temperatures over a few thousand degrees Celsius. The Sun, like most stars, is almost entirely plasma, making plasma the most abundant state of matter in the universe.
Answered by Rik Sargent