Death cross and Golden cross

In Technical Analysis, a Death cross happens when the short term moving average crosses long term moving average and goes below it. This is seen as the start of a bearish market (but is not always the case based on historical trends)

A Golden cross happens when short term moving average crosses long term moving average and goes above it. This is seen as the beginning of bullish market.

See the S&P 500 index over years as an example. The short term is 50 day moving average and long term is 200 day moving average. Source: finance.yahoo.com

An hourly trend during 12/6-12/7/2018 shows formation of the crosses. Source: finance.yahoo.com

Read this marketwatch.com article on 12/7: https://www.marketwatch.com/story/heres-what-the-dow-coming-close-to-a-death-cross-really-means-for-stocks-2018-12-06