The three phases of matter are the solid, liquid, and gas phase. A solid has a definite shape and volume. The molecules within a solid are very close together and cannot move around. A liquid has a definite volume, but takes the shape of the container it is in. In a liquid, the molecules are still close together, but they can move around slowly. A gas fills the entire volume of the container it is in. In a gas, the molecules are spaced apart, move around freely, and rapidly.