A sustained recession is known as an economic depression. A short-lived one is often called an economic correction. However, many theorists including John Kenneth Galbraith believe that there is no reasonable distinction between the three, other than a desire to downplay risk of a panic. In the nineteenth century, such theorists point out, business cycle events of the same magnitude were typically called "crises" or "panics".
To avoid all these politically loaded terms, the more neutral term 'recession' is to be preferred, despite the overly-specific technical economics definition. The politics implied by the current definition, including the assumption of relevance of Gross National Product to human well-being, or the desirability/necessity of reporting by quarter-years, are challenged in some theories of a larger political economy consisting of voting, market, and other activities.
That said, there is little challenge to the idea that GNP (or GDP) are related to job availability in a wage-employment economy, nor to the idea that business confidence[?] and consumer spending[?] tend to decrease during a recession, which is usually a crisis of trust.
Recessions are mostly caused by economic shocks. The greatest, worldwide recession that humanity has ever experienced was the Great Depression (late 1920s and 1930s); other notable recessions include the Oil Crisis[?] in the 1970s. In both cases the reliability of prior pricing decisions and leadership quality was in question, and money tended to seek 'safe havens' (like real estate) and avoid speculative investments exposed to the 'crisis'.
Q: Money has to be explicitly created or destroyed. So what happens to all the money during a recession. Suppose you have 250 million people living in a huge hall and there is a recession in the hall, no money went into or left the hall. Where did all the money go?
Q: Isn't a recession a normal part of the business cycle?
The fact that parties and theories compete to set policies in the vote market, and have the power to set definitions on such terms as 'recession' or 'depression', and explain their meaning to the public as authority figures, leads to larger questions in political economy, specifically those explored in political choice theory.
An example of the importance of this is the Great Depression itself. When President Franklin D. Roosevelt entered office in 1932, he was intending to continue a relatively conservative fiscal policy to placate his business critics (Herbert Hoover in particular had warned him that any controversial early action would affect business confidence[?] very adversely). However, after Black Monday[?] Roosevelt was forced to change his mind, and instituted the "New Deal" economic reforms to stave off any future depressions.
To date none have happened. At least, none we are allowed to call "depressions", regardless of their impact on actual human lives.
It is an open question whether a "depression" can even be noticed at all under the terminology in use among technical economists today. Galbraith among others thought it could not, and that the terminology was merely exercise in concealment - a potent criticism from an economist who was a central part of that Administration during the war years.