>>103423462Sheng nü (leftover women, as in food) are over 30s women who didn't marry partners.
The key thing (IIRC) is that they never found partners that fit their specifications (your classic 6,6,6 but whatever the Chinese version is).
So they kept waiting for their 6'1 Shanghai CEO prince to sweep them off their feet and are now femcels.
It's a little overstated, the Chinese marriage rate for over 30 women is still better than a lot of countries apparently. But there are just a lot of them in absolute terms because china is fucking huge.