a bull market is a financial market with rising asset prices that are fueled by investors' optimism, confidence and expectations. while bull markets are partly based on actual investment performance, they are also partly based on investor psychology. the bull market gets its name from the way a bull thrusts its horns upward. when investors are optimistic about investment performance, they are called bullish. the term bull market can be applied to a market as a whole such as the overall stock market or bond market or to a specific security such as shares in a publicly traded company or a particular commodity such as ? crude oil. a bull market is a long-term trend, lasting several years. it usually occurs when a country's overall economic performance is strong and unemployment is low. in a bull market, demand for securities exceeds supply, which drives share prices up. people also have more money to spend in a bull market, which improves companies' profitability and further drives up share prices. the united states has experienced 12 bull markets since the great depression. bull markets last for a different lengths of time and experience gains at different paces. the strongest one lasted from december 1987 through march 2000 and experienced a 582% gain over 148 months. this was also the longest bull market. the shortest began in 1932 and lasted just 14 months, gaining 177%. the bull market that included the housing bubble, which lasted from october 2002 through october 2007 ? a 101.5% gain over 60 months. the median bull market experiences gains of about 3% per month.