Breadth of market

A technique used in technical analysis that attempts to gauge the direction of the overall market by analyzing the number of companies advancing relative to the number declining. Positive market breadth occurs when more companies are moving higher than are moving lower, and it is used to suggest that the bulls are in control of the momentum. Conversely, a disproportional number of declining securities is used to confirm bearish momentum.

Investopedia Says:
A large number of advancing issues is a sign of bullish market sentiment and is used to confirm a broad market uptrend. Traders will specifically look at the number of companies that have created a 52-week high relative to the number that created a 52-week low because this data can provide longer term information about whether the bullish or bearish trend will continue.

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Discover the indicators that measure the force of the bulls and bears, telling you what a simple price chart cannot. Market Breadth: A Directory Of Internal Indicators
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Developed in 1967 by Richard Arms, this volume-based breadth indicator can be applied over various time periods. Introduction to the Arms Index