(N/A) Compression is a region of high pressure and high density in a longitudinal wave where particles of the medium are closer together.
Rarefaction is a region of low pressure and low density in a longitudinal wave where particles of the medium are farther apart.
When an object vibrates,it moves back and forth rapidly. When it moves forward,it pushes the air particles in front of it,creating a region of high pressure and density called a compression. When it moves backward,it creates a region of low pressure and density behind it,called a rarefaction. As the object continues to vibrate,these alternating regions of compressions and rarefactions propagate through the medium as a sound wave.