Before 1968, there were many techniques that high jumpers used to get over the bar, though with most, you'd jump forward and land on your feet. Then Richard Fosbury won the Olympic gold with his "Fosbury flop" technique which involves jumping backward and landing on your back. Ever since, the Fosbury flop technique has been the most widespread and effective technique in high jumping, and in fact, it's the technique you have probably seen on TV if you've watched high jumping.
A Fosbury Flop moment happens to an industry or area when a new innovation, approach or technique is introduced that then becomes the dominant option. These are breakthrough improvements that change the course of history.