See the sound. Check out this famous video and see for yourself. The sound can be seen, it draws the correct patterns, depending on the frequency.
Sound is a longitudinal, mechanical wave. Sound can travel through any medium, but it cannot travel through a vacuum. There is no sound in outer space. Sound is a variation in pressure. A region of increased pressure on a sound wave is called a compression (or condensation). A region of decreased pressure on a sound wave is called a rarefaction (or dilation).
Waves are created when energy is transferred through a medium like water, air, or objects.