In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer.
Sound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids) are also longitudinal waves.
Longitudinal waves show area of compression and rarefaction. In the animation, the areas of compression are where the parts of the spring are close together, while the areas of rarefaction are where they are far apart.
