Sound is a mechanical wave that propagates as a disturbance through a medium, like air. The speed of sound refers to how fast this disturbance travels. The source creates the initial vibration, and the listener receives it, but neither travels 350 meters. The air molecules themselves only vibrate locally; they do not travel the full distance. The energy and the wave pattern, which is the disturbance, move through the medium.

Therefore, the distance of 350 m in one second is travelled by the disturbance.