The document discusses the three states of matter - solid, liquid, and gas. A solid retains a fixed shape and volume, with molecules tightly packed and not moving. A liquid flows easily and is compressible, with molecules close together and moving. A gas is compressible and flows easily, with molecules spread far apart and moving fast. Examples are given for solids like ice and diamonds, liquids like water and molten iron, and gases like water vapor and helium.