A sound wave requires a medium. This is because sound waves transmit through vibrations. Without a medium, per say, a vacuum, there would be no sound because there would be no medium; no particles to vibrate off of.
All waves need a medium in order to travel. Some waves must travel through a substance. The substance is known as the medium, and it can be solid, liquid or gas. Sound waves and seismic waves are like this: they must travel through a medium.
