wavelength (longitudinal wave) – the distance from one compression to the next compression or from one rarefaction to the next rarefaction

Note: Longitudinal wave think sound.

The meaning of longitudinal wavelengths is self explanatory, see below:

The wavelength of a longitudinal wave is the distance between two identical points on the wave, typically measured as the distance from the centre of one compression (where particles are closest) to the centre of the next compression, or from one rarefaction (where particles are spread out) to the next. It represents one complete longitudinal wave cycle and is often denoted by the Greek letter lambda (λ).

A bass guitar would typically give a note with a wavelength of 6.8 metres but a violin would typically have a wavelength of 0.17 metres.