A longitudinal wave is associated with sound. These waves travel in the same direction they are vibrating. Imagine a line of people. If you pushed the person in the back you would see a moving wave as people bumped into each other. (Then you would see a fight so don't do it)
The longitudinal wave has different names for the parts of the wave.
Another thing to note is the equation for a wave. v = λf
v represents the velocity of the wave, it is how fast the wave is traveling through the medium. Its units are a distance over time (m/s)
λ (lambda) This represents the wavelength, its units are a distance (km, m, mm, nm, ...)
f This represents the frequency. Its unit is Hz or 1/s