Your definition would exclude basically every crash other than https://en.wikipe...

Your definition would exclude basically every crash other than https://en.wikipedia.org/wiki/Wall_Street_Crash_of_1929, which entailed a “89.2% loss for the index”. Even then, it came back eventually.

When the "flash crash" happened in 2010 it was a 9% drop. https://en.wikipedia.org/wiki/2010_flash_crash

$22 is half the average for the months preceding the drop, and 1/3 the peak, with a sustained drop for more than two weeks straight. That’d be called a crash by pretty much anyone.