Here's why:

* Waves are disturbances that travel through a medium or space. They transfer energy from one point to another without permanently displacing the medium itself.

* Think of a ripple in a pond. The water molecules themselves don't travel far; they just oscillate up and down. It's the energy that moves outward in a wave pattern.

* Light waves are a good example. They are electromagnetic waves that carry energy through space, but they don't require a medium to travel.

While waves don't carry matter, they can influence the movement of matter. For example, ocean waves can move sand and rocks along the shore.