Sart is a name for the settled inhabitants of Central Asia which has had shifting meanings over the centuries.
There are several theories about the origin of the term. It may be derived from the Sanskrit sārthavāha (सार्थवाह), meaning "merchant, trader, caravan leader", a term supposedly used by nomads to describe town-dwellers, according to Vasily Bartold, Gerard Clauson, and most recently Richard Foltz.
The earliest known use of the term is in the 1070 Turkic text Kutadgu Bilig "Blessed Knowledge", in which it refers to the settled population of Kashgar. Then, the term apparently referred to all settled Muslims of Central Asia, regardless of language.
Rashid al-Din Hamadani in the Jami' al-tawarikh writes that Genghis Khan commanded for Arslan Khan, prince of the Karluks, to be given the title "Sartaqtai", which he considered to be synonymous with Tajik.
A 13th-century Mongolian source, The Secret History of the Mongols, states that the Mongols called people from Central Asia, most notably Khwarazm, "Sartuul". In Mongolian, "Sar" (сар / ᠰᠠᠷᠠ) means "moon," so sart or sarta would mean "ones with (flag with) moon" since the Muslims had a crescent moon symbol on their flags. One of the Mongol tribes living in Zavkhan Province, Mongolia is made up of descendants of merchants from Khwarazm who resided in Kharkhorin and is still called Sartuul.
In the post-Mongol period we find that Ali-Shir Nava'i refers to the Iranian people as Sart Ulusi ("Sart people"), and for him Sart tili ("Sart language") was a synonym for the Persian language. Similarly, when Babur refers to the people of Margilan as "Sarts", it is in distinction to the people of Andijan who are Turks, and it is clear that by this he means Persian-speakers. He also refers to the population of the towns and villages of the vilayat of Kabul as "Sarts".
Similarly, Babur wrote in the Baburnama in 1525, "In the country of Kābul there are many and various tribes. Its valleys and plains are inhabited by Tūrks, Aimāks, and Arabs.