About the definition of a solid

At the start of the lecture, I wrote that a solid is something:

1. That has a definite shape and size that remains unchanged as long as external conditions are unchanged. It can stay on its own and does not need a container to hold it.
2. It obeys Hooke’s law.
3. The atoms/molecules in it have a fixed, ordered arrangement that is observed over length scales large compared to their size.

I think even neutral fluids and plasma can be treated as an assembly of nuclei and electrons; especially plasma. One usually does not need quantum mechanics to study behaviour of plasma.