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"ov" suffix is an indicator of a male patronymic. This person's father's name was Itsko. This name should be preceded by a given name of the person, e.g., Aron Itskov Dunner means Aron son of Itsko Dunner. Sometimes you will see the male version of the patronymic with the "ovich" suffix, instead of "ov", but it means exactly the same thing. For females the suffix is "ova" or "ovna" - Sura Itskova (or Itskovna) Dunner (Sura daughter of Itsko Dunner).
In some cases these patronymics became last names, e.g., Aronov, Abramov.