When combined, 小三 (xiǎosān) creates the label “little third one,” a powerfully concise and contemptuous term for a person, usually a woman, who is having an affair with a married or committed man.
The term “小三” exploded in popularity in the early 2000s, coinciding with China's rapid economic growth. As new wealth created new social dynamics, stories of powerful men keeping mistresses became a frequent topic in media and public discourse. The term became a tool for public shaming, encapsulating societal disapproval of infidelity. Unlike the English word “mistress,” which can sometimes sound archaic or even carry a veneer of glamour, “小三” is modern, raw, and almost exclusively negative. It's less about a long-term, semi-official arrangement (as “mistress” can sometimes imply) and more of a label of public condemnation. While in the West, the focus of blame for an affair might be split or fall heavily on the cheating spouse, in Chinese public opinion, the “小三” often bears a disproportionate amount of social scorn. This is tied to the cultural importance of marital stability and the concept of 面子 (miànzi), or “face,” as infidelity brings immense shame and loss of face to the entire family, especially the legal wife (原配 yuánpèi).
“小三” is a term you'll hear constantly in informal settings. It's a cornerstone of modern slang.