Starting from the Middle Ages, the term Tati was used not only for the Caucasus but als for north-western Iran, where it was extended to almost all of the local Iranian languages except of Persian and Kurdish.
Currently the term Tati and Tati language is used to refer to a particular group of north-western Iranian dialects (Chali, Danesfani, Hiaraji, Hoznini, Esfarvarini, Takestani, Sagzabadi, Ebrahimabadi, Eshtehardi, Hoini, Kajali, Shahroudi, Harzani) in Iranian Azerbaijan, as well as south of it in the provinces of Qazvin and Zanjan. These dialects have a certain affinity to the Talysh language as one of the descendants of the Old Azari language.
The use of the name Tati to two different Iranian languages erroneously suggests that the Caucasian Tats also live in Iran.
^Paul, Ludwig (1998a). The position of Zazaki among West Iranian languages. In Proceedings of the 3rd European Conference of Iranian Studies, 11-15.09.1995, Cambridge, Nicholas Sims-Williams (ed.), 163-176. Wiesbaden: Reichert.
^Andrew Dalby, Dictionary of Languages: the definitive reference to more than 400 languages, Columbia University Press, 2004, pg 496.
^"Azari, the Old Iranian Language of Azerbaijan," Encyclopaedia Iranica, op. cit., Vol. III/2, 1987 by E. Yarshater. External link: 
^Языки мира. Иранские языки. Северо-западные иранские языки. с. 106-107. М., Индрик, 1999 г.