Bull Market

The mirror image of a bear market, and the same convention applies: 20 percent is the customary line rather than a defined one. The word comes from the upward thrust of a bull's horns.

In ordinary use the phrase has drifted well past its definition. People say bull market to mean a stretch of rising prices and general optimism, without measuring anything, which is why the term appears far more often in commentary than the arithmetic behind it does.

Like its opposite, a bull market can only be dated backwards, because the low it is measured from is only identifiable once prices have stopped falling. That is worth remembering whenever a headline announces that one has begun.