In equities market, it is a state to which values of stocks, bonds and other derivatives are headed for the ground. Bear markets are governed by a fundamentally bad economy which follows right after a cycle of full employment. Investors in a bear market are pessimistic about the current investment opportunities as values of equities continue to fall.
Since corrections are a normal occuring event in a capitalist setting, bear markets are supposed to be a very favorable entry point for investing. On the short trader side, it is a period of high profit as their borrowed stocks are now cheaper to replace.