Tocharian denotes two closely related Indo-European languages, Tocharian A and Tocharian B, now considered distinct. They were first discovered in documents from Chinese Turkestan along the Silk Road. Key sites include Turfan in the north and Kučā to the west, with a third major site at Tumšuq forming the western boundary. Tocharian A is confined to Turfan and Qārāšahr, while Tocharian B spans from Turfan to Tumšuq.

Most Tocharian documents date from the sixth and eighth centuries AD and are translations of Buddhist texts. Secular documents exist only in Tocharian B, leading some to believe Tocharian A may have become extinct as a spoken language, preserved only for liturgical use. The name "Tocharian" was proposed by F. W. K. Müller in 1907 and by Sieg and Siegling in 1908, but is now thought a misnomer. Tocharian is a centum language, challenging the geographical division of centum and satem dialects.

In terms of geography, Tocharian is the easternmost ancient Indo-European language and is a centum language, breaking the expected west-east division. It has a reduced phonetic inventory with all voiceless stops.