A stock market crash is a sudden dramatic decline of stock prices across a major cross-section of a stock market, resulting in a significant loss of paper wealth. Crashes are driven by panic selling and underlying economic factors. They often follow speculation and economic bubbles.

A stock market, equity market, or share market is the aggregation of buyers and sellers of stocks, which represent ownership claims on businesses; these may include securities listed on a public stock exchange as well as stock that is only traded privately, such as shares of private companies that are sold to investors through equity crowdfunding platforms. Investments are usually made with an investment strategy in mind.