Rarefaction
（重定向自Rarifying）
![An example of rarefaction is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.](/Images/godic/202502/06/Onde_compression_impulsion_1d_30_petit3806.gif")
Rarefaction is the reduction of an item's density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave (see picture).