A death cross is a shorter term moving average, typically the 50-day, cuts down through the slower average, traditionally the 200-day. False signals are common, therefore other technicals should be consulted.
British banking group Lloyds (LYG) generated a Death Cross last week with the 50-day exponential moving average slipping under the 200-day. The previous signal of the same type in September 2017 failed but then conditions were different, momentum, as depicted by the 14-day RSI, oversold with a value around 30. However, the present signal has a greater chance of fulfilment since momentum has room to unwind.