Semu 色目 or semuren 色目人, literally "people of separate categories", was a Yuan-period 元 (1279-1368) designation for persons of Central and Western Asia (including Europeans). The word is a general term without further distinguishing between sub-categories of these types of foreigners. The word semu was first used in the Tang Code Tanglü shuyi 唐律疏議 with the meaning "many separate categories", but the expression is probably a Chinese rendering of the Mongol term qari irgen "foreigners, strangers" in a dualistic system that just separated between Mongols and non-Mongols, while the four-classes system (sidengren zhi 四等人制) was perhaps its application to the political situation in China. Hu (2013) analysed the use of the word semu before the Yuan period and found out that from the early Song period on, the expression semuren was used for persons with extraordinary family names, the so-called "various (i.e. irregular) family names" (zaxing 雜姓). The Japanese scholar Funada Yoshiyuki 船田善之 (1999) had found out that a Mongolian analogue of the Chinese expression semuren did not exist, nor did foreign accounts like Rašīd ad-Dīn's (1247-1348) book Ǧāmiʿ at-tawārīḫ (Ch. Shiji 史集) nor Marco Polo's (1254-1324) Divisament du Monde (The Travels of Marco Polo) mention the four social classes or a distinct and coherent class of "Central Asians" (semuren). Analysis of household registers of the time and their classification rather demonstrated that the category semuren included Mongols, Buddhist Uyghurs (Weiwu'er 畏兀兒), Kitans, "Muslims" (Huihui 回回) and Chinese from Hexi 河西 altogether, with no ethnic segregation. Funada concludes that the concept of semuren is Chinese, and not Mongolian.
The contemporary author Tao Zongyi 陶宗儀 (1329-1410), author of Nancun chuogeng lu 南村輟耕錄, holds that there were 31 types of Semuren, while the historian Qian Daxin 錢大昕 (1728-1804), writing his Yuanshi shizu biao 元史氏族表 much later, speaks of 23 categories. The problem with these numbers is that the Mongols did never clearly and consequently discern between various ethnic groups.
The most important groups of Semuren were Tanguts (Tangwu 唐兀), Naiman 乃蠻, Önggüds (Wanggu 汪古, Yonggudai 雍古歹), Muslim Uyghurs (Huihui), Buddhist Uyghurs, Qangli (Kangli 康里), Kipchaks (Qincha 欽察), Alans (Asu 阿速), Qarluqs (Halalu 哈剌魯, Geluolu 葛邏祿), Tibetans (Tubo 吐蕃, Tubote 土伯特), Tuvans (Tuba 禿八), Argyns (A'erhun 阿兒渾), Circassians (Che'erkesi 撒耳柯思, Che'erge 撒儿哥), Russians (Woluosi 斡羅思) or Kashmirians (Qieshimi’er 怯失迷兒, Qishimi'er 乞失迷兒). Jews and Nestorian Christians also belonged to the Semu class, and of course, Europeans merchants like the Polo family.
Semuren played an important role in the conquest and administration of the Yuan empire, and therefore settled in all important places of China. The Mongols gave them the second rank of the four classes of people, above the Northern (Hanren 漢人) and the Southern Chinese (Nanren 南人). Members of Semuren class served in high positions in the Yuan empire, like generals, members of the civilian administration, or as experts in various fields like astronomy, mathematics or ballistics. Others were entrepreneurs and cooperated with the Yuan government. One of the famous Semuren people is Ahmad Fanākatī (Ch. Ahama 阿合馬, 1242-1282), chief counsellor or Manager of Governmental Affairs in the Palace Secretariat (zhongshu pingzhang zhengshi 中書平章政事).
In all official functions, Semuren were preferred over Chinese, and could obtain posts from which Chinese were excluded, like daruγači 達魯花赤. While only Mongols were allowed to serve as daruγači, Chinese were given xxx 漢人任總管，色目人任同知，以便互相監督. Semuren enjoyed nearly the same privileges as Mongols in the field of state examinations, and were punished with lighter sentences than Chinese, and had the right to be judged by the xxx 大宗正府, just like the Mongols. On the other hand, these privileges only pertained to the upper class of the Semuren, and not the commoners, which were treated much in the same way as Chinese subjects.
After the demise of the Yuan empire, many Semuren remained in China. Many of them were Muslims and retained their creed in the coming generations. One of the most famous offspring of Muslim Semuren is Admiral Zheng He 鄭和 (1371-1433 or 1435), whose ancestors had migrated to Yunnan during the Yuan period. The share of Muslims among the Semuren was so large that the two words were nearly synonyms.