Lexicon
Bull Market
The long stretch where the trend, and the mood, both point up.
A bull market is a sustained period of rising prices across a broad market, generally understood as a rise of 20% or more from a prior low, typically accompanied by improving economic conditions and rising investor confidence.
Unlike a bear market's more precisely used 20%-decline convention, "bull market" gets applied a bit more loosely in everyday use — sometimes to describe any extended uptrend, sometimes reserved specifically for the recovery and expansion that follows a bear market's bottom. Either way, the core idea is the same: a stretch of time where rising prices and growing optimism are reinforcing each other.
What a bull market actually includes
A rising broad market doesn't mean every stock is rising, or rising equally. Bull markets are typically led by a subset of sectors or companies performing especially well, while others lag or even decline, and the index-level number can mask a lot of variation underneath it. Treating a bull market as evidence that "everything is working" is a common oversimplification.
The risk hiding inside optimism
The later stages of a bull market are where investor behavior tends to get riskiest — rising prices breed confidence, confidence breeds larger bets and less scrutiny, and the memory of the last decline fades. None of that means a bull market is about to end on any predictable schedule; it means the discipline that mattered in the bear market matters just as much, if quieter, in the bull market that follows it.