Quhistan (Persian: قهستان) or Kohistan (کهستان, "mountainous land") was a region of medieval Persia (Iran), essentially the southern part of Khurasan. Its boundaries appear to have been indeterminate, and the term generally seems to have been applied loosely. The area tended to be ruled as part of Khurasan however, experience some periods of autonomy.
Dagestan in the North Caucasus was priorly and originally named "Quhistan", which has the same meaning as Dagestan: dağ and kuh are the Turkic and Persian words for "mountain", respectively. -istan is Persian suffix meaning "land [of]".