A bear market occurs when the broad markets face a prolonged drop in prices. Market cycles are measured from peak to trough. If a broad market index, such as the S&P 500, falls at least 20% from its most recent high, the markets have entered a bear market. 

In contrast, the bull market begins when the closing price gains 20% from its previous low. Bear and Bull markets are commonly occurring. As of June 2023, the S&P 500 data shows that the markets have experienced 28 bear and 28 bull markets since 1928. The duration of the bear and bull market varies significantly over the years.