A recession is a significant decline in activity across the economy, lasting longer than a few months. It is visible in industrial production, employment, real income and wholesale-retail trade. The technical indicator of a recession is two consecutive quarters of negative economic growth as measured by a country's gross domestic product (GDP), although the National Bureau of Economic Research (NBER) does not necessarily need to see this occur to call a recession.
Aside from two consecutive quarters of GDP decline, economists assess several metrics to determine whether a recession is imminent or already taking place. These indicators are divided into two categories: leading indicators and lagging indicators. Leading indicators materialize before a recession is officially declared. Perhaps the most common leading indicator is contraction in the stock market. Declines in broad stock indices, such as the Dow Jones Industrial Average (DJIA) and Standard & Poor's (S&P) 500 index, often appear several months before a recession takes shape. This was the case in 2007, when the market began declining in August, four months ahead of the official recession in December 2007.
Lagging indicators of a recession include the unemployment rate. Though the Great Recession began in December 2007, the unemployment rate still indicated full employment -- a rate of 5% or lower -- four months later. The unemployment rate began declining in May 2008 and did not recover until several months after the recession ended in June 2009.
A depression is a deep and long-lasting recession. While no specific criteria exist to declare a depression, unique features of the last U.S. depression, the Great Depression of the 1930s, included a GDP decline in excess of 10% and an unemployment rate that briefly touched 25%.