Semu () is the name of a caste established by the Yuan dynasty. The 31 Semu categories referred to people who came from Central and West Asia. They had come to serve the Yuan dynasty by enfranchising under the dominant Mongol caste. The Semu were not a self-defined and homogeneous ethnic group per se, but one of the four castes of the Yuan dynasty: the Mongols, Semu (or Semuren), the "Han" (Hanren in Chinese, or all subjects of the former Jin dynasty, Dali Kingdom and Koreans) and the Southerners (Nanren in Chinese, or all subjects of the former Southern Song dynasty; sometimes called Manzi). Among the Semu were Buddhist Turpan Uyghurs, Tanguts and Tibetans; Nestorian Christian tribes like the Ongud; Alans; Muslim Central Asian Turkic peoples including the Khwarazmians and Karakhanids; West Asian Arab, Jewish, Christians and other minor groups who are from even further west.
Contrary to popular belief among both non-Chinese and Chinese, the term "Semu" (interpreted literally as "color-eye") did not imply that caste members had "colored eyes" and it was not a physical description of the people it labelled. It in fact meant "assorted categories" (各色名目, gè sè míng mù), emphasizing the ethnic diversity of Semu people.
The 31 Semu categories referred to people who came from Central and West Asia. They had come to serve the Yuan dynasty by enfranchising under the dominant Mongol caste. The Semu were not a self-defined and homogeneous ethnic group per se, but one of the four castes of the Yuan dynasty: the Mongols, Semu (or Semuren), the "Han" (Hanren in Chinese, or all subjects of the former Jin dynasty, Dali Kingdom and Koreans) and the Southerners (Nanren in Chinese, or all subjects of the former Southern Song dynasty; sometimes called Manzi). Among the Semu were Buddhist Turpan Uyghurs of Qocho, Tanguts and Tibetans; Nestorian Christian tribes like the Ongud; Alans; Muslim Central Asian Persian and Turkic peoples including the Khwarazmians and Karakhanids; West Asian Jewish and other minor groups who are from even further Europe.