The action of a solid changing to a liquid state through the application of heat is called melting.

Here's a breakdown:

* Solid: In a solid, particles are closely packed together and vibrate in fixed positions.

* Heat: When heat is added to a solid, the particles gain kinetic energy and vibrate more vigorously.

* Melting: As the particles vibrate more, they overcome the forces holding them together in a fixed arrangement. This allows them to move around more freely, transitioning from a solid to a liquid state.

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