depression

In Meteorology, an area of low atmospheric pressure. It is a region of the atmosphere where the pressure is lower than in the surrounding areas, increasing from the center outward. On surface synoptic maps it is represented by a set of closed isobars increasing in value as one moves outward from its center (pressure minimum). On upper-air maps, the isohypses take on a similar shape, forming a sunken area that constitutes a (barometric) depression, hence its name. It is synonymous with low, cyclone, and gale/low-pressure system.