After all, glass as a material was known about long before its molecular physics was understood. Macroscopically materials exhibit a very wide range of behaviours. Solids, liquids and gases are ideal behaviours characterised by properties such as compressibility, viscosity, elasticity, strength and hardness. Materials do not always behave according to such ideals. For example it is possible to take water from being a liquid to a gas at high pressure without passing through a phase transition so at some stage it must be between an ideal liquid and an ideal gas.
Some people say that there is no clear distinction between a solid and a liquid in general.
A solid, they claim, should just be defined as a liquid with a very high viscosity. According to another point of view, this ignores a distinction between viscosity of liquids and plasticity of solids. An ideal Newtonian liquid deforms at a rate which is proportional to stresses applied and its viscosity. For arbitrarily small stresses a viscous liquid will flow. Molasses, pine pitch and Silly Putty are examples of liquids with very high viscosity which flow very slowly under only the force of their own weight.