longitudinal wave

This term is a technical descriptor used primarily in physics and acoustics to distinguish a specific type of wave motion from transverse waves. While a transverse wave moves perpendicular to the direction of energy transfer (like a plucked guitar string), a longitudinal wave involves a series of compressions and rarefactions that move in the same direction as the wave itself.

In practical application, the most common example is sound. Because it describes a physical mechanism of propagation, the term is used in formal scientific contexts, textbooks, and engineering specifications rather than in casual conversation.