An amorphous solid does not have a definite geometric or crystalline shape. It is a solid in which there is no long-term order in the positions of the atoms. Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous ceramic, many polymers are amorphous, and even foods such as cotton candy are amorphous solids.
Solids and liquids are both forms of condensed matter; both are composed of atoms in close proximity to each other. But their properties are, of course, enormously different. While a solid material has both a well-defined volume and a well-defined shape, a liquid has a well-defined volume but a shape that depends on the shape of the container. Stated differently, a solid exhibits resistance to shear stress while a liquid does not. Externally applied forces can twist or bend or distort a solid’s shape, but (provided the forces have not exceeded the solid’s elastic limit) it “springs back” to its original shape when the forces are removed. A liquid flows under the action of an external force; it does not hold its shape. These macroscopic characteristics constitute the essential distinctions: a liquid flows, lacks a definite shape (though its volume is definite), and cannot withstand a shear stress; a solid does not flow, has a definite shape, and exhibits elastic stiffness against shear stress.