Map from Kashgari's Diwan
, showing the distribution of Turkic tribes.
The first known mention of the term Turk (Old Turkic: 𐱅𐰇𐰼𐰰 Türük or 𐱅𐰇𐰼𐰰:𐰜𐰇𐰛 Kök Türük Chinese: 突厥, Old Tibetan: duruggu/durgu (meaning "origin"), Pinyin: Tūjué, Middle Chinese (Guangyun): [tʰuot-küot]) applied to a Turkic group was in reference to the Göktürks in the 6th century. A letter by Ishbara Qaghan to Emperor Wen of Sui in 585 described him as "the Great Turk Khan." The Orhun inscriptions (735 CE) use the terms Turk and Turuk.
Previous use of similar terms are of unknown significance, although some strongly feel that they are evidence of the historical continuity of the term and the people as a linguistic unit since early times. This includes Chinese records Spring and Autumn Annals referring to a neighbouring people as Beidi.
During the first century CE, Pomponius Mela refers to the "Turcae" in the forests north of the Sea of Azov, and Pliny the Elder lists the "Tyrcae" among the people of the same area. There are references to certain groups in antiquity whose names could be the original form of "Türk/Türük" such as Togarma, Turukha/Turuška, Turukku and so on. But the information gap is so substantial that we cannot firmly connect these ancient people to the modern Turks. Turkologist András Róna-Tas posits that the term Turk could be rooted in the East Iranian Saka language or in Turkic. However, it is generally accepted that the term "Türk" is ultimately derived from the Old-Turkic migration-term 𐱅𐰇𐰼𐰰 Türük/Törük, which means "created", "born", or "strong", from the Old Turkic word root *türi-/töri- ("tribal root, (mythic) ancestry; take shape, to be born, be created, arise, spring up") and conjugated with Old Turkic suffix 𐰰 (-ik), perhaps from Proto-Turkic *türi-k ("lineage, ancestry"), from the Proto-Turkic word root *töŕ ("foundation, root; origin, ancestors"), possibly from a Proto-Altaic source *t`ŏ̀ŕe ("law, regulation"). This etymological concept is also related to Old Turkic word stems 'tür' ("root, ancestry, race, kind of, sort of"), 'türi-' ("to bring together, to collect"), 'törü' ("law, custom") and 'töz' ("substance").
The earliest Turkic-speaking peoples identifiable in Chinese sources are the Dingling, Gekun (Jiankun), and Xinli, located in South Siberia. The Chinese Book of Zhou (7th century) presents an etymology of the name Turk as derived from "helmet", explaining that this name comes from the shape of a mountain where they worked in the Altai Mountains. According to Persian tradition, as reported by 11th-century ethnographer Mahmud of Kashgar and various other traditional Islamic scholars and historians, the name "Turk" stems from Tur, one of the sons of Japheth (see Turan).
During the Middle Ages, various Turkic peoples of the Eurasian steppe were subsumed under the identity of the "Scythians". Between 400 CE and the 16th century, Byzantine sources use the name Σκύθαι (Skuthai) in reference to twelve different Turkic peoples.
In the modern Turkish language as used in the Republic of Turkey, a distinction is made between "Turks" and the "Turkic peoples" in loosely speaking: the term Türk corresponds specifically to the "Turkish-speaking" people (in this context, "Turkish-speaking" is considered the same as "Turkic-speaking"), while the term Türki refers generally to the people of modern "Turkic Republics" (Türki Cumhuriyetler or Türk Cumhuriyetleri). However, the proper usage of the term is based on the linguistic classification in order to avoid any political sense. In short, the term Türki can be used for Türk or vice versa.