There are also stock market bubbles.
In a normal market, investors buy stock in a company because they anticipate that future profits will become dividends and they believe the value of the company's assets will increase. Sometimes, though, a "herd mentality" sets in and too many brokers rush to buy, driving prices like mercury up a thermometer to levels that prove unrealistic. Eventually it becomes clear that further increases are not forthcoming and price deterioration develops, followed by a swift drop. When this happens to too many companies in aggregate, it is called a stock market crash. A recent stock market bubble was the "dot-com" bubble. The buzz about the economic possibilities of the Internet encouraged investors to fund the creation of many dotcom companies - too many it turned out. For several years, dozens of entrepreneurs sought to duplicate for themselves the results of those that had come before.