In the stock market, it means buying an asset after it drops in price.

When your favorite stock keeps tanking and you keep buying until you run outta money, hoping it rebounds and make you crazy rich.

To purchase a stock or commodity during a price decline. Became popular during the post-housing bubble quantitative easing trend, where stocks were guaranteed to rise until a new dawn of American capitalism magically occurred or, alternatively, the money supply exploded resulting in uncontrollable inflation.