1. Recession
In economics, a recession is a business cycle contraction which results in a general slowdown in economic activity. Macroeconomic indicators such as GDP (gross domestic product), investment spending, capacity utilization, household income, business profits, and inflation fall, while bankruptcies and the unemployment rate rise. In the United Kingdom, it is defined as a negative economic growth for two consecutive quarters.
Recessions generally occur when there is a widespread drop in spending (an adverse demand shock). This may be triggered by various events, such as a financial crisis, an external trade shock, an adverse supply shock or the bursting of an economic bubble. Governments usually respond to recessions by adopting expansionary macroeconomic policies, such as increasing money supply, increasing government spending and decreasing taxation.

2. In the United States, the Business Cycle Dating Committee of the National Bureau of Economic Research (NBER) is generally seen as the authority for dating US recessions. The NBER defines an economic recession as: "a significant decline in economic activity spread across the economy, lasting more than a few months, normally visible in real GDP, real income, employment, industrial production, and wholesale-retail sales.” Almost universally, academics, economists, policy makers, and businesses defer to the determination by the NBER for the precise dating of a recession's onset and end.
In the United Kingdom, recessions are generally defined as two consecutive quarters of negative economic growth, as measured by the seasonal adjusted quarter-on-quarter figures for real GDP. The exact same recession definition applies for all member states of the European Union.

3. A recession has many attributes that can occur simultaneously and includes declines in component measures of economic activity (GDP) such as consumption, investment, government spending, and net export activity. These summary measures reflect underlying drivers such as employment levels and skills, household savings rates, corporate investment decisions, interest rates, demographics, and government policies.
Economist Richard C. Koo wrote that under ideal conditions, a country's economy should have the household sector as net savers and the corporate sector as net borrowers, with the government budget nearly balanced and net exports near zero. When these relationships become imbalanced, recession can develop within the country or create pressure for recession in another country. Policy responses are often designed to drive the economy back towards this ideal state of balance.

4. Some recessions have been anticipated by stock market declines
Some recessions have been anticipated by stock market declines. In Stocks for the Long Run, Siegel mentions that since 1948, ten recessions were preceded by a stock market decline, by a lead time of 0 to 13 months (average 5.7 months), while ten stock market declines of greater than 10% in the Dow Jones Industrial Average were not followed by a recession.
The real-estate market also usually weakens before a recession. However real-estate declines can last much longer than recessions. Since the business cycle is very hard to predict, Siegel argues that it is not possible to take advantage of economic cycles for timing investments. Even the National Bureau of Economic Research (NBER) takes a few months to determine if a peak or trough has occurred in the US.

5. Unemployment is particularly high during a recession
Unemployment is particularly high during a recession. Many economists working within the neoclassical paradigm argue that there is a natural rate of unemployment which, when subtracted from the actual rate of unemployment, can be used to calculate the negative GDP gap during a recession. In other words, unemployment never reaches 0 percent, and thus is not a negative indicator of the health of an economy unless above the "natural rate," in which case it corresponds directly to a loss in gross domestic product, or GDP.
The full impact of a recession on employment may not be felt for several quarters. Research in Britain shows that low-skilled, low-educated workers and the young are most vulnerable to unemployment in a downturn. After recessions in Britain in the 1980s and 1990s, it took five years for unemployment to fall back to its original levels. Many companies often expect employment discrimination claims to rise during a recession