On DJI Go 4 app it is just an experience level or flight time. Not sure it has any useful meaning. My flight stats are all screwed up. I've been to 1640ft many times but it says max altitude 83ft, and other parameters it has for my info are way off also, max speed, total distance, etc. I'd trust that data about as much as a career politician seeking reelection lol.
I just noticed that my "growth of value" got reset to 1 :-/. Oh well.
Agree w/ @cderoche, the flight stats seem a bit buggy. My "footprints" don't show anything at all, for example (I think it's supposed to show flags from countries you've flown in).