The word "rarefaction" refers to the reduction or decrease in the density or concentration of something. It is often used to describe a situation where something becomes less crowded, less compressed, or less tightly packed together. Full definition
In particular, performance work can be conceptually fraught in the museum when artists have circumvented the commodification and rarefaction of art by creating ephemeral works -LSB-.....] (dailyserving.com)
Dividing the samples into those from before 1980 and after, the researchers used rarefaction to be able to compare samples collected using different methods and under divergent conditions. (scientificamerican.com)
Buoyancy waves generated by winds flowing over orography can produce vertically propagating compression and rarefaction waves that may be related to the narrow haze layers. (science.sciencemag.org)