Bear market

A bear market is described as being accompanied by widespread pessimism. Investors anticipating further losses are often motivated to sell, with negative sentiment feeding on itself in a vicious circle. The most famous bear market in history was preceded by the Wall Street Crash of 1929 and lasted from 1930 to 1932, marking the start of the Great Depression. A milder, low-level, long-term bear market occurred from about 1973 to 1982, encompassing the stagflation of U.S. economy, the 1970's energy crisis, and the high unemployment of the early 1980s.
Prices fluctuate constantly on the open market; a bear market is not a simple decline, but a substantial drop in the prices of the majority of stocks in a given market over a defined period of time. According to The Vanguard Group, "While there’s no agreed-upon definition of a bear market, one generally accepted measure is a price decline of 20% or more over at least a two-month period."