If you hear the phrase "its a bullish market" or a "bearish market" its simply referring to whether there is a rising or falling trend in the market.
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a bullish market refers to a market that has a long-term up trend.
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a bearish market is referring to a market which has a long-term downtrend.
A market usually gets labeled bullish or bearish after it has risen or fallen by over 20%.
Example
DJ30 Bullish market | June 2006 - June 2007
(chart courtesy of Telechart 2007)
It should appear obvious but a general rule you should follow is to buy in a bull market and sell in a bear market, especially when swing or position trading. Its always hard work making money going against the overall trend.