Definitions of depression:

• a mental state characterized by a pessimistic sense of inadequacy and a despondent lack of activity
• a long-term economic state characterized by unemployment and low prices and low levels of trade and investment
• natural depression: a sunken or depressed geological formation
• sad feelings of gloom and inadequacy
• a period during the 1930s when there was a worldwide economic depression and mass unemployment
• low: an air mass of lower pressure; often brings precipitation; "a low moved in over night bringing sleet and snow"
• depressive disorder: a state of depression and anhedonia so severe as to require clinical intervention
• a concavity in a surface produced by pressing; "he left the impression of his fingers in the soft mud"
• angular distance below the horizon (especially of a celestial object)
• pushing down; "depression of the space bar on the typewriter"