Sound wave: The longitudinal wave in an elastic medium that produces an audible sensation is called a sound wave.
As sound waves are longitudinal waves, the air particles vibrate to and fro in the direction of propagation of sound.
It is a wave of compression and rarefaction.
Compressions and rarefactions are part of a sound wave.
Compression: A region in a longitudinal wave where the particles are closest together is called compression. Compression has high density and high pressure
Rarefaction: A region in a longitudinal wave where the particles are furthest apart is called rarefaction. The rarefaction has a low density and low pressure