The particles of the medium vibrate about their equilibrium position in a direction parallel to the direction of propagation of the wave is called a longitudinal waves.
Longitudinal waves require a medium with only elasticity of volume (or Bulk modulus) for its propagation. In this type of wave motion, the waves travel through a medium in the form of compression and rarefaction.
The region of high pressure is called compression and the region of low pressure is called rarefaction. For example, Sound waves in the tube.