A leftover woman (Mandarin: Shèngnǚ 剩女) is a term used in China and elsewhere in East Asia to describe women over 30 who are femcel or unable/unwilling to find an appropriate husband. This has created some confusion, because there's supposed to be an oversupply of men in the Far East, some of whom are the 'leftover men' (Mandarin: Shèngnán 剩男). Some may be lesbocel, and therefore often unable to form long-term sexual relationships due to prevalent social norms. Claims have been made that they may be volcel, however, there are many reasons for which many may be involuntarily single, mainly tied to East Asian culture.
Women in East Asia are under strong societal pressure to marry men richer and older than them, and East Asian women generally have less casual sex and pre/non-marital sexual relationships than their equivalents in the West. Higher-status men in East Asia consider women over 30 to have hit the wall physically, and Asian parents will often disapprove of their son choosing a woman over 30, due to fertility concerns.
In China, there are divergent concerns for higher-status and lower-status leftover women. Higher status leftover women tend to have ambitious careers and high status lives, and therefore want to find handsome men with modern gender norms, and higher social status than them; if they can't find these, they may choose to remain volcel, or be forced to look for lower-status men; however, these low-status males often end up being bitter towards having a higher-status wife, and (as low social status is correlated with being rural and less educated) may have more traditional gender norms, which cause high levels of tension in marriages. Some women opt for inceldom after abusive marriages. For lower-status women, especially in parts of the country with less sex disparity (due to uneven implementation of the one-child policy), there is a higher chance that unattractive poor women will be rejected and considered unmarriageable at very young ages, and these leftover women are often more likely to be genuine femcels, especially as norms against sexual impropriety are stronger in poor, rural areas.