A shockwave is essentially a pressure disturbance that propagates rapidly through a MEDIUM.

It can be defined thus: A large-amplitude compression wave, as that produced by an explosion or by supersonic motion of a body in a medium which just a formal version of the first sentence.

A clinically useful shockwave is effectively a controlled explosion, and when it enters the tissues, it will be reflected, refracted, transmitted and dissipated like any other energy form. The energy content of the wave will vary and the propagation of the wave will vary with tissue type. Just like an ultrasound wave, the shock wave consists of a high-pressure phase followed by a low pressure (or relaxation) phase. When a shock wave reaches a 'boundary', some of the energy will be reflected and some transmitted.