Here's a breakdown:

* Solid: A state of matter where particles are tightly packed and have a fixed shape and volume.

* Heat: A form of energy that causes the particles within a substance to vibrate and move faster.

* Melting: The process where heat energy increases the vibrations of the particles in a solid to the point where they break free from their fixed positions and transition into a liquid state.

The temperature at which a solid melts is called its melting point.