Definition of 'Bear'
An investor who believes that a particular security or market is headed downward. Bears attempt to profit from a decline in prices. Bears are generally pessimistic about the state of a given market.
Investopedia explains 'Bear'
For example, if an investor were bearish on the S&P 500 they would attempt to profit from a decline in the broad market index. Bearish sentiment can be applied to all types of markets including commodity markets, stock markets and the bond market.
Although you often hear that the stock market is constantly in a state of flux as the bears and their optimistic counterparts, "bulls", are trying to take control, do remember that over the last 100 years or so the U.S. stock market has increased an average 11% a year. This means that every single long-term market bear has lost money.