Vortex

A vortex [Latin vortex, vortic-, variant of vertex, from vertere, to turn.] is a spiraling motion of material particles around a common center of rotation. Especially a whirling mass of water or air that sucks everything near it toward its center. Vortices are one of the most important research areas in fluid dynamics. This comes mainly from two facts. First, vortices have a great impact on the development of a flow in many cases. Second, although a colloquial definition (as above) can be given, there exists no exact mathematical definition of a vortex, its extent or even its center. Thus, finding vortices is challenging and no method fitting for all situations exists.

Examples
Vortices in nature:
 * Tornado
 * Hurricane
 * Wake vortex created at the tip of a wing of an aircraft
 * Swirling water that runs through the drain of a basin