A bull market is a financial market where prices of instruments ( e.g.
stocks ) are, on average, increasing.
Investors might thus depend to a certain extent upon the market continuing
to rise and are thus motivated to buy stock in anticipation of capital
gains. A bear market may be fueled by sound economic fundamentals or by
speculation. Speculation that is not based on sound economic fundamentals
can result in stocks being over-valued. An exaggerated bull market fueled by
speculation is called a stock market bubble.
The opposite of a bull market is a bear market where the market is falling.