Which type of wave is characterized by particle movement that is parallel to the wave direction?

A longitudinal wave is defined by the movement of particles in a medium that occurs parallel to the direction of the wave's travel. In this type of wave, such as sound waves, particles of the medium compress and then rarefy in the same direction that the wave propagates, creating regions of compression and rarefaction. This parallel motion is a key characteristic that distinguishes longitudinal waves from transverse waves, where particle movement occurs perpendicular to the direction of wave propagation. In summary, the correct answer identifies the behavior of particles in relation to wave movement, which aligns perfectly with the properties of longitudinal waves.