In historiographic writing on the period, the term was meant as a prince in Kievan Rus' who was excluded from succession to the Kievan throne because his father had not held the throne before, as exemplified by Yaroslav the Wise's two youngest sons becoming izgoi.
[1] In Kievan Rus', as well as Appanage and early Muscovite Russia, collateral succession, rather than linear succession, was practiced, with the throne being passed from the eldest brother to the youngest brother and then to cousins until the fourth in line of succession (not to be confused with "fourth cousins") in a generation before it was passed on to the eldest member of the senior line if his father had held the Kievan throne.
[3][4][5] The term is also found in the expanded version of the Russkaya Pravda, where it meant an orphan or exile;[6] thus, an izgoi prince is in some sense seen as an "orphaned" or "exiled" prince since he was left outside of the succession to the Kievan throne.
Furthermore, in spite of his excluded status, Vseslav briefly seized the throne of Kiev in 1069 but held it only six months before he was ousted.
Since Vladimir had died in 1052, two years before his father, Yaroslav the Wise (d. 1054), he had never held the Kievan throne, and Rostislav was an izgoi.