What It Means
A bull market is a sustained period where prices are rising, or widely expected to rise, usually accompanied by investor optimism and steady buying volumes. There's no single official threshold — unlike a bear market's rough 20% marker — but the term generally applies when an index has been trending higher for months, not days.
How It Works
Bull markets tend to build gradually: early gains draw in more buyers, rising prices reinforce confidence, and that confidence pulls in even more capital, including from investors who were sitting out. Sentiment indicators — rising trading volumes, expanding new-stock highs, easier IPO listings — usually confirm what price is already showing. The risk isn't spotting a bull market late; it's assuming it continues indefinitely and sizing positions as if a correction can't happen.
Warning
A few strong up-weeks after a dip don't automatically mean a new bull market has started — traders who chase every rally risk buying right before a pullback resumes.