A vortex can refer to a number of different things, all of which deal with motion. In physics, it is the name given to matter that is whirling around a specific center. In nature, a vortex is a type of phenomenon such as a tornado. In a laboratory, it is a specific piece of machinery used for mixing. In fiction, the term usually refers to a type of dimensional gateway.
A vortex in physics is an occurrence where matter whirls in a spiral pattern. The matter usually has to have a specific level of cohesion and flexibility for this to occur, such as that associated with liquids and gases. The pressure at the core of the spiral is the least, the outer edges the most. A line called the vortex line can be drawn down the center of this area.
Vortexes, or vortices, often occur in nature. Dust devils, water spouts, tornadoes, and hurricanes are all examples. They are caused by air flow and clouds, and are visible due to either the water vapor or solid matter that is sucked into them. Vortices that occur in water are called whirlpools. Whirlpools are rare in nature, but usually occur due to either rough water or the creation of lower pressure areas in the water. The term vortex can also be associated with various magnetic and astronomical occurrences.
A vortex is also a helpful piece of laboratory equipment. In a lab, it is usually a simple, hand-sized device that is set on top of a table; a test tube containing liquid is gently pressed against the top of the device. The device rotates the test tube in a way that creates a vortex inside of it. This stirs the contents of the test tube extremely well, and is why the device can be found in most chemistry labs.
Vortices have also found their way into fiction. In science fiction, they are often described as galactic anomalies such as wormholes that allow travel either over large distances or through time. In fantasy, they usually act as portals to other dimensions. In ancient myths and legends, vortices tend to be massive whirlpools that destroy ships.