The material that waves travel through is called a medium.

Here's a breakdown:

* Mechanical Waves: These waves require a medium to travel. Think of sound waves traveling through air, water waves through water, or seismic waves through the Earth.

* Electromagnetic Waves: These waves do not require a medium and can travel through a vacuum, like light traveling from the sun to Earth.

So, while the word "medium" is often associated with mechanical waves, it's a general term used for any substance that waves can travel through.