An area of low atmospheric pressure which has a closed circulation. In the northern hemisphere the circulation is counterclockwise, and in the southern hemisphere it is clockwise.

Because cyclonic circulation and relatively low atmospheric pressure usually coexist, the terms cyclone and low are often used interchangeably. Also, because cyclones are often accompanied by inclement and sometimes destructive weather, they are frequently referred to as storms.

Tropical cyclones are called hurricanes or typhoons, and cyclones that form in the higher latitudes are called barometric depressions.