Here's why:

* Waves don't transport matter. Think about a wave on the ocean. The water itself doesn't travel all the way to the shore; it just moves up and down.

* Waves carry a disturbance. This disturbance can be a change in pressure (like in sound waves), a change in electric and magnetic fields (like in light waves), or a change in the position of particles (like in water waves).

* The disturbance transfers energy. The energy is what travels from the source (where the disturbance originated) to the receiver (where the disturbance is detected).

Example: Imagine dropping a pebble into a pond. The pebble creates ripples, which are waves. The ripples carry energy outward, causing the water to move up and down. The water itself doesn't travel across the pond, but the energy of the wave does.