This document discusses the four states of matter: solid, liquid, gas, and plasma. It describes the key properties of each state. Solids have a fixed shape and volume, with particles tightly packed and vibrating in place. Liquids have indefinite shapes but fixed volumes, with particles tightly packed but able to slide past one another. Gases have indefinite shapes and volumes, with particles far apart and moving freely. Plasmas are gases whose particles are ionized, making them electrically conductive and responsive to magnetic fields. Plasma is the most common state of the Sun and can be found in flames, lightning, and auroras.