There is no numerically specific definition of a stock market crash but the term commonly applies to steep double-digit percentage losses in a stock market index over a period of several days. Crashes are often distinguished from bear markets by panic selling and abrupt, dramatic price declines. Bear markets are periods of declining stock market prices that are measured in months or years. Crashes are often associated with bear markets, however, they do not necessarily go hand in hand. The crash of 1987, for example, did not lead to a bear market. Likewise, the Japanese bear market of the 1990s occurred over several years without any notable crashes.
What Happens When the Stock Market Crashes?
Tulip Mania (in the mid-1630s) is often considered to be the first recorded speculative bubble. Historically, early stock market bubbles and crashes have also their roots in socio-politico-economic activities of the 17th-century Dutch Republic (the birthplace of the world's first formal stock exchange and market), the Dutch East India Company (the world's first formally listed public company), and the Dutch West India Company (WIC/GWIC) in particular. As Stringham & Curott (2015) remarked, "Business ventures with multiple shareholders became popular with commenda contracts in medieval Italy (Greif, 2006, p. 286), and Malmendier (2009) provides evidence that shareholder companies date back to ancient Rome. Yet the title of the world's first stock market deservedly goes to that of seventeenth-century Amsterdam, where an active secondary market in company shares emerged. The two major companies were the Dutch East India Company and the Dutch West India Company, founded in 1602 and 1621. Other companies existed, but they were not as large and constituted a small portion of the stock market (Israel  1991, 109–112; Dehing and 't Hart 1997, 54; de la Vega  1996, 173)."
What Is China's Stock Market Called?
On October 24, many of the world's stock exchanges experienced the worst declines in their history, with drops of around 10% in most indices. In the US, the DJIA fell 3.6%, i.e. not as much as other markets. Instead, both the US dollar and Japanese yen soared against other major currencies, particularly the British pound and Canadian dollar, as world investors sought safe havens. Later that day, the deputy governor of the Bank of England, Charles Bean, suggested that "This is a once in a lifetime crisis, and possibly the largest financial crisis of its kind in human history."