A depression, also known as a 'low' can be recognised on a weather chart by an area of closely spaced isobars, often in a roughly circular shape, where pressure is lower than surrounding areas. They are often accompanied by fronts. In the Northern Hemisphere winds blow around depressions in an anticlockwise direction. The lowest pressure occurs at the middle of a depression, this is known as the 'low pressure centre'. Depressions are often associated with strong winds and heavy rain and are nearly always accompanied by fronts.

http://www.met-office.gov.uk/education/curriculum/lesson_pla...