1. In general, a point or limited area of locally lower elevation in a particular surface. 2. In meteorology, an area of low pressure; a low or trough. This is usually applied to a certain stage in the development of a tropical cyclone, to migratory lows and troughs, and to upper-level lows and troughs that are only weakly developed. This use of the term is most common in the European literature. See V-shaped depression. 3. Same as depression angle. 4. See wet-bulb depression, dewpoint spread.