Mahmud Kashgari defined the title Shad as an heir apparent a step above Yabgu.
According to Movses Kagankatvatsi, Böri Shad was a 7th-century Western Turkic Khaganate prince and an ishad, or a ruler of a principality, a nephew of Tong Yabgu Kagan, and a son of Moho shad, who may have been a Yabgu of the Khazars.
The title "Shad" left prominent marks in the Asian toponymy, and on many mints of Middle Asia Late Antique and Early Middle Age coins, like Shad Bagh in northern Lahore in Punjab, Pakistan, and early Bukhara, Uzbekistan coins.
When the last Eastern Turkic Kagan Illig suffered a defeat from the Tang empire in 630 CE, the Chinese annals recorded that only after the last royal prince, a certain Yshbara-Shad Sunishi (沙缽略設蘇尼失) and Ilig's uncle, surrendered, did the Eastern Türkic Kaganate cease to exist.
[7][8] Gumilyov explained the Shad's full title as "mighty prince of [the tribe] Shunishi"[9][a]