Here's a breakdown:

* Melting Point: The temperature at which a solid changes state to a liquid.

* Crystal Solid: A solid with a highly ordered, repeating arrangement of atoms, molecules, or ions.

When you heat a crystal solid, you're adding energy to its particles. This energy causes the particles to vibrate more vigorously, eventually overcoming the forces holding them in their fixed positions. At the melting point, the solid transitions to a liquid state.