A disturbance that transfers energy from place to place is known as a wave. The substance that carries the wave is known as the medium.
When the medium is repeatedly acted upon by a vibrating source, the first particle of the medium is displaced, which in turn displaces the next particle, which displaces its neighbor, and so on. In this way, the energy from the source is transferred through the medium, while the actual matter comprising the medium is not transferred. A wave is known as an energy transport phenomenon because a wave transfers energy through the medium but only temporarily displaces the particles of the medium itself.