The phenomenon that results from the rapid changes in tissue and fluid pressure that occur with the passage of a projectile, resulting in serious injury to internal organs distant to the actual path of the bullet, is known as what?

Cavitation.

Explanation:

In penetrating trauma a permanent cavity is produced by the passage of an object through the body. Cavitation is the result of the exchange of energy between the moving object and the tissues, this kind of trauma is usually related to gun shots and stab wounds.

When a moving object encounters an obstacle, an energy exchange occurs between them. When it is concentrated in a small area, it may exceed the surface tension of the tissue and penetrate it. The exchange of energy between moving objects and tissues results in cavitation. It depends on the area and shape of the missile, the tissue density and speed of the projectile at the moment of impact. The area and shape may vary as they deviate, and the fragment may produce so-called secondary projectiles.