The mirror of golden-cross. It gets heavy press attention because the name is dramatic and the calculation is simple enough to explain in a headline.
As a signal it is extremely late by construction: both averages are backward-looking, so the cross typically occurs well after a decline is underway and often near a short-term low. Studies of index data generally find that forward returns after a death cross are not reliably worse than average, and sometimes better.
Its practical value is descriptive. It tells you the market has been weak for a while, which you could already see. Treating it as a sell signal on the day it prints has a poor historical record, and it is a good example of indicator-lag being mistaken for insight.
Related: golden-cross, moving-average-crossover, indicator-lag, simple-moving-average, trend-following