Here's why:

* Propagation means to spread or transmit something, and that's exactly what waves do. They transmit energy and information through a medium or space.

* The wave itself doesn't travel, but rather the disturbance it creates moves. Think of a ripple in a pond: the water molecules themselves don't travel across the pond, but the disturbance created by the ripple does.

So, the term wave propagation describes the movement of this disturbance, whether it's a water wave, a sound wave, or an electromagnetic wave.