Pahlavi is an exclusively written form of various Middle Iranian languages, derived from the Aramaic script. It features Aramaic words used as heterograms (called huzwārišn, "archaisms").
Pahlavi compositions have been found for the dialects/ethnolects of Parthia, Persis, Sogdiana, Scythia, and Khotan. Independent of the variant for which the Pahlavi system was used, the written form of that language only qualifies as Pahlavi when it is both Aramaic-derived and features huzwārišn.