In the Ottoman Empire, a millet was a separate court of law pertaining to "personal law" under which a confessional community (a group abiding by the laws of Muslim Sharia, Christian Canon law, or Jewish Halakha) was allowed to rule itself under its own laws. Despite frequently being referred to as a "system", before the nineteenth century the organization of what are now retrospectively called millets in the Ottoman Empire was far from systematic. Rather, non-Muslims were simply given a significant degree of autonomy within their own community, without an overarching structure for the 'millet' as a whole. The notion of distinct millets corresponding to different religious communities within the empire would not emerge until the eighteenth century. Subsequently, the existence of the millet system was justified through numerous foundation myths linking it back to the time of Sultan Mehmed II (r. 1451-81), although it is now understood that no such system existed in the fifteenth century. After the Ottoman Tanzimat (1839–76) reforms, the term was used for legally protected religious minority groups, similar to the way other countries use the word nation. The word millet comes from the Arabic word millah (ملة) and literally means "nation". The millet system has been called an example of pre-modern religious pluralism.
The term millet, which originates from the Arabic milla, had three basic meanings in Ottoman Turkish: religion, religious community and nation. The first sense derives from Quranic usage and is attested in Ottoman administrative documents into the 19th century. Benjamin Braude has argued that before the period of 19th-century reforms, the word millet in the sense of religious community denoted the Muslim religious community or the Christians outside of the Ottoman empire. This view is supported by Donald Quataert. In contrast, Michael Ursinus writes that the word was used to refer to non-Muslim subjects of the Ottoman empire even before that time. The term was used inconsistently prior to the 19th century.