Solid - Any material or substance that is not a liquid or gas. A solid has a definite shape and volume. A cube, sphere, or pyramid are all solids, having length, width and depth. They are not hollow. Liquid - A state of matter.
Liquids flow and always take up the shape of the vessel into which they are poured.
Gas - A state of matter that has a mass but no shape. It fills and takes the shape of a container. Air is a mixture of gases. The material of which all things in the universe are made. Milliken Publishing Company, 1984.