The material through which a mechanical wave travels is called the medium.

Here's why:

* Mechanical waves need a medium: Unlike electromagnetic waves (like light), mechanical waves require a physical substance to propagate. They can't travel through a vacuum.

* Examples of mediums: Think of sound waves traveling through air, water waves moving through water, or seismic waves passing through the Earth.

* How the medium is involved: The particles of the medium oscillate or vibrate as the wave passes, transferring energy without transferring the medium itself.

Let me know if you'd like to explore any of these concepts further!