In economics, a period of exceptionally low output and investment, with high unemployment. Specifically, the term describes two periods of crisis in world economy 1873–96 and 1929–39, also known as panics.
The term is most often used to refer to the world economic crisis precipitated by the Wall Street crash of 29 Oct 1929, when millions of (inflated and margined) dollars were wiped off US stock values by panic selling in a matter of hours. This forced the closure of many US banks whose reserves were involved in stock speculation and led to the recall of US overseas investments. This loss of US credit had serious repercussions on the European economy, especially that of Germany (still recovering from World War I), and led to a steep fall in the levels of international trade as countries attempted to protect their own economies.
Despite unprecedented federal government intervention under President Franklin D Roosevelt's New Deal, the economy began a real recovery only after the rearmament programs of the late 1930s and 1940s boosted employment and output.

ETYM Latin depressio: cf. French dépression.
Emotional state characterized by sadness, unhappy thoughts, apathy, and dejection. Sadness is a normal response to major losses such as bereavement or unemployment. After childbirth, postnatal depression is common. However, clinical depression, which is prolonged or unduly severe, often requires treatment, such as antidepressant medication, cognitive therapy, or, in very rare cases, electroconvulsive therapy (ECT), in which an electrical current is passed through the brain.
Periods of depression may alternate with periods of high optimism, over-enthusiasm, and confidence. This is the manic phase in a disorder known as manic depression or bipolar disorder. A manic depressive state is one in which a person switches repeatedly from one extreme to the other. Each mood can last for weeks or for months. Typically, the depressive state lasts longer than the manic phase.
Depression costs the US around $12.4 billion each year in treatment. Another $23.8 billion is paid for by employers, arising from absenteeism and lost productivity.
(meteorology) or cyclone or low. In meteorology, a region of low atmospheric pressure. In mid latitudes depression forms as warm, moist air from the tropics mixes with cold, dry polar air, producing warm and cold boundaries (fronts) and unstable weather—low cloud and drizzle, showers, or fierce storms. The warm air, being less dense, rises above the cold air to produce the area of low pressure on the ground. Air spirals in toward the center of the depression in a counterclockwise direction in the northern hemisphere, clockwise in the southern hemisphere, generating winds up to gale force. Depressions tend to travel eastward and can remain active for several days.
A deep depression is one in which the pressure at the center is very much lower than that round about; it produces very strong winds, as opposed to a shallow depression in which the winds are comparatively light. A severe depression in the tropics is called a hurricane, tropical cyclone, or typhoon, and is a great danger to shipping; a tornado is a very intense, rapidly swirling depression, with a diameter of only a few hundred feet or so.
1. A concavity in a surface produced by pressing; SYN. impression, imprint.
2. A long-term economic state characterized by unemployment and low prices and low levels of trade and investment; SYN. slump, economic crisis.
3. A mental state characterized by a pessimistic sense of inadequacy and a despondent lack of activity.
4. Angular distance below the horizon (especially of a celestial object).
5. Pushing down.
6. Sad feelings of gloom and inadequacy.

Tinted glassware machine-produced during the 1930s

Lowering of a solution’s freezing point below that of the pure solvent; it depends on the number of molecules of solute dissolved in it. For a single solvent, such as pure water, all solute substances in the same molar concentration produce the same lowering of freezing point. The depression d produced by the presence of a solute of molar concentration C is given by the equation d = KC, where K is a constant (called the cryoscopic constant) for the solvent concerned.
Measurement of freezing-point depression is a useful method of determining the molecular weights of solutes. It is also used to detect the illicit addition of water to milk.