A vortex ring (or toroidal vortex), is a donut-shaped region of circulation that moves through the fluid medium. A vortex ring tends to move in the direction perpendicular to the plane of the ring, possibly extending out a considerable distance. The movement of the fluid can be classified as poloidal (related to the short route around a torus), across the circular axis of the donut, in such a way that the inner part of the ring moves faster toward the front side.