In terms of sound, what does compression refer to?

Compression in the context of sound refers to an increase in the density of air molecules. When a sound wave travels through a medium, it generates areas of compression and rarefaction. During compression, air molecules are pushed closer together, which raises the local pressure and density of the air. This is a crucial aspect of how sound waves propagate through mediums.

Understanding sound waves begins with recognizing that they involve longitudinal waves, where the displacement of the medium is in the same direction as the wave travel. The areas of compression alternate with areas of rarefaction, where air molecules become less densely packed. This cycle of compression and rarefaction is essential for the transmission of sound, as it allows energy to travel through the medium in the form of waves.

In summary, since the definition of compression accurately captures the mechanism of sound wave propagation via increased density of air molecules, this choice is the correct answer.