A bull market is a prolonged stretch in which prices trend upward and investor confidence is high. There is no official starting gun, but a rise of roughly 20% or more from a recent low is the conventional marker that one is under way. The mood tends to feed on itself: rising prices draw in more buyers, which pushes prices higher still.
Bull markets can run for months or years, and they often last far longer than nervous investors expect. They also end. Every bull market in history has eventually given way to a correction or a bear market, and the turn is rarely announced in advance. Strong recent returns are not a promise of future ones.
The practical lesson is to separate the trend from the decision. A rising market makes almost any purchase look smart in hindsight, which is exactly when it pays to keep position sizes sensible and avoid chasing momentum with money you cannot afford to lose.
Worked example
US equities ran a multi-year bull market through the 2010s, while crypto has seen several shorter, sharper bull runs — each followed by a steep drawdown.
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This definition is general education, not investment advice. Markets — especially crypto — are volatile and you can lose money. Please read our disclaimer and see our methodology.