A wave that travels through a medium?

Answer 1

We know that a mechanical wave requires a medium through which to travel. The source puts the energy into the medium, and it propagates. A sound wave is a good example of this, and we can contrast it with an electromagnetic wave (like light). Light can travel through a vacuum; it doesn't require a medium for its propagation.

Answer 2

Mechanical waves travel through a medium. Sound is a mechanical wave that can travel through the mediums of air, water, rocks, etc.