Acoustic waves are a type of longitudinal wave that propagate by means of adiabatic compression and decompression. Longitudinal waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle velocity, particle displacement and sound intensity. Acoustic waves travel with the speed of sound which depends on the medium they're passing through.

 For transverse waves the wave motion is perpendicular (at right-angles) to the wave direction:

_  Mexican (stadium, audience) waves,

_  Shear waves in solids (seismic S-waves),

_  Electromagnetic waves (light, radio, microwave, bluetooth, etc.),

_  Rope waves,

_  Love waves (a shear surface wave).

For longitudinal waves the wave motion is aligned with the wave direction:

_  Stop-go traffic waves on busy motorways caused by braking,

_  Compression waves in solids (seismic P-waves),

_  (Ultra)sound waves.

 Propagating waves are a means by which energy can be transferred from one point to

another without transfer of matter.

 Ultrasound waves are longitudinal, compression waves, that can be periodic or pulsed, propagate at roughly 1500 m/s in water or biological tissue, can leave the medium unchanged (diagnostic ultrasound), but at higher intensities can also change it (therapeutic ultrasound).