Breadth-of-the-market definitions

The number of stocks that are participating in either the market’s upward or downward movement. If the stock market rises during a trading session and a large number of stocks also rise, then the market has good breadth. Inversely, if the market rises, but only a relatively small number of stocks rise, the upward price movement is said to lack breadth. The same is true of a declining market. Breadth often is measured by the advance-decline ratio, which compares the numbers of stocks rising against the number of those that are falling.