rarefaction /rer′əfak″shən/ , 1. reductions in density of a tissue. 2. reduction in the density of a medium, such as air, which is denser close to the earth and the pull of gravity and has a reduced density at higher stratospheric levels. 3. (in physical science) reductions in density of a medium (air, pressure, wave motion) at a location in the medium accompanying cyclical pressure reductions during the passage of a sound wave. For example, the prong of a tuning fork vibrates in the air, and air adjacent to the prong is compressed. When the prong springs back in the opposite direction, it leaves an area of reduced air pressure.
