Longitudinal wave: this wave produces vibrations in the direction it moves, that is, it pushes the particles in the medium towards their direction of propagation.
Unlike another type of wave that is the transverse wave, which produces vibration in a direction perpendicular to its direction of propagation.
So the wave mentioned in the statement is a longitudinal wave because the displacement of the particles is in the direction of the wave.
An example of this type of wave are sound waves, which are transmitted by vibrations in the particles of the medium (like air) in their direction of the movement of the wave.
