A solid is really a quantum system, and must be described by quantum physics. No way around that. This video tries to convince you about this. When the video pauzes to ask you a question, provide the answer in the forum underneath and then continue watching:
When the video stops, asking you for your spontaneous definition of a solid, submit your definition to this forum:
Once you finished this video, go back to the forum hereabove, pick one contribution that has no comments yet, identify which aspects of the definition given there agree or do not agree with the definition given in the video, and submit this as a reply to that post (please be respectful to the person who submitted the definition). If you get stuck at calculating the total energy for the cartoon hydrogen crystal, you may watch the solution here.