What it means
Crossovers work in trends and whipsaw in ranges.
In practice
The cross is a slow, simple statement about the long-term trend: the average price of the last 50 days has risen above the average of the last 200. Investors use it as a broad filter for whether a market is in an up or down phase.
It gets attention in the news when it happens on major indices or Bitcoin, which is part of why traders keep an eye on it.
What to watch for
By the time two long averages cross, a large part of the move has already happened. In sideways markets the averages cross back and forth, producing a string of losing signals.