Frangistan (Persian: فرنگستان) was a term used by Muslims and Persians in particular, during the Middle Ages and later historical periods to refer to Western or Latin Europe.
Frangistan literally means "Land of the Franks", from Farang which is the Persianized form of Frank plus the suffix -istan coming from the Persian language. During the Crusades, the Muslims of the Middle East came to call all Christendom Franks, originally the name for inhabitants of the largest of the Christian realms in Europe, Francia, which gave its name to the kingdom of France (while its eastern part came to be known as the Holy Roman Empire).
As the Franks (French) formed a substantial part of the force of the First Crusade, and Old French became the dominant language in the crusader states of the 12th century (notably the Principality of Antioch), the term Frank as used in the Levant could mean any Western European Christian (whether Frankish, Saxon, Flemish, etc.). Frangistan was no clearly defined area and may have referred to any land perceived to be Christian by contemporary Muslims.
In a similar way, Greek Christians were "Rumis", named for Rûm (derived from "Rome", i.e. the Byzantine Empire). Conversely, Christians generally called Muslims Saracens or Moors, both after the names of more localized tribes, in Arabia and Mauretania, respectively.
The term Frangistan was still in use in the time of the Ottoman Empire, in sources as late as the 17th century. However, in Persia it remained in use until the end of the Qajar dynasty as observed in various correspondences and administrative documents of that era to refer to European countries. Other derivatives of this word such as Farang (noun), Farangi (adjective), and compound words like Farangi Ma'āb (literally French-styled), are used with lower frequency in Modern Persian, though without any negative connotation. In Hindi in present-day India, all Europeans in general are still referred to as Firang.