Stocks are any equity securities traded on a stock exchange, the value of which fluctuates due to the supply and demand for such securities. Stocks are often grouped in a specific sector and can be viewed as representative of the broader marketplace.
Due to the subprime mortgage-related financial crisis of 2008/2009, stocks dropped significantly in value and the entire global financial system was at risk of collapse. Only after dramatic intervention by central banks around the world were stocks able to stabilize after the shock.
The financial crisis caused the Great Recession in the Main Street economy. Stocks hit a low in March of 2009.
With dramatic monetary policy intervention, stocks recovered from their collapse and were able to move up strongly thereafter. The last two years in particular produced strong capital gains for equity investors. Stocks today are vulnerable to another correction because of this recent price strength.