Noun
The act or process of rarefying; the state of being rarefied; -- opposed to condensation; as, the rarefaction of air.
Source: Webster's dictionarya sound wave causes periodic rarefactions in its medium Source: Internet
Hence, inertial cavitation can occur even if the rarefaction in the liquid is insufficient for a Rayleigh-like void to occur. Source: Internet
The opening between the reed and the mouthpiece makes very little difference to the reflection of the rarefaction wave. Source: Internet
This rarefaction wave travels back up the tube (image 2). Source: Internet