A longitudinal wave moves energy that is to the direction of the wave's movement.

In longitudinal waves, the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave. Mechanical longitudinal waves are also called compressional or compression waves because they produce compression and rarefaction of a medium when traveling through the medium. They are also called pressure waves, because they produce increases and decreases in pressure of the medium. Sound waves is an example of longitudinal wave.