Imagine a pulse propagating in a string. As the wave travels each segment of the string moves up and down perpendicular to the direction of propagation. At the macroscopic level, we observe a transverse wave that moves along the string, and the individual motion of the segments is not relevant.. In contrast, at the microscopic level, we see discrete particles undergoing oscillatory motion perpendicular to the motion of the wave.
In a string, or a solid, or a fluid, the collective motion of the particles determine the velocity of sound in the medium, as well as the thermal transport properties.
coupled oscillators