Longitudinal wave
Also called Compression wave
A longitudinal wave is one in which the disturbance is parallel to the direction the wave travels, producing regions of compression and rarefaction. Sound is the AP example, and longitudinal waves cannot be polarized.
AP Physics 2 EK 14.1.A.5: in a longitudinal wave, the direction of the disturbance is parallel to the direction of propagation of the wave. Push one end of a slinky along its length and the compression runs down it, while each coil only shuffles back and forth about its own resting place.
Sound is the case the exam uses. EK 14.1.A.5.i says sound waves are modeled as mechanical longitudinal waves. EK 14.1.A.5.ii names the parts: the regions of high and low pressure in a sound wave are called compressions and rarefactions.
Amplitude looks different here. There is no visible crest, so EK 14.1.A.6.i allows the amplitude of a longitudinal pressure wave to be given as the maximum increase or decrease in pressure from equilibrium pressure. Louder means a bigger pressure swing (EK 14.1.A.6.ii), not a faster wave.
It cannot be polarized. EK 14.3.A.2.ii states this outright, and it is the cleanest way to tell a longitudinal wave from a transverse wave in an exam question. The oscillation already lies along the direction of travel, so there is no perpendicular plane left to select from.
Being mechanical, sound needs a medium (EK 14.1.A.2), unlike an electromagnetic wave. EK 14.1.A.3.iii adds that in a given medium the speed of sound increases with temperature.