Bull Markets and Bear Markets : These terms describe long-term trends, not short -term changes. Bull and bear markets are usually measured in years. As Navin. The bear market definition is exactly the opposite of a bull market. It's a market where quarter after quarter and the market is moving down about 20 percent. It is the opposite of a bull market, in which asset prices consistently rise. One common measure says that a bear market exists when at least 80% of all stock.