A solid will put up some resistance to shear forces, up to the plastic limit. A liquid gives zero resistance to a constant shear force after enough time. What t

A solid will put up some resistance to shear forces, up to the plastic limit. A liquid gives zero resistance to a constant shear force after enough time. What this means is that a solid might approximate a sphere but it will still at the limit have some level of roughness (even with something as extreme as a neutron star), while a liquid will in principle always move towards a perfect sphere under gravity alone.