rarefaction

The condition of being rarefied.

A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.

The region in which this occurs.

The act or process of rarefying or making rare, or of expanding or distending a body or mass of matter, whereby the bulk is increased, or a smaller number of its particles occupy the same space; also, the state or condition so produced: opposed to condensation.

The act or process of rarefying; the state of being rarefied; — opposed to condensation.

a reduction in the density of a material, especially that of a fluid

a decrease in the density of something