The terms Muslim world and Islamic world commonly refer to the Islamic community, which is also known as the Ummah. This consists of all those who adhere to the religious beliefs, politics, and laws of Islam or to societies in which Islam is practiced. In a modern geopolitical sense, these terms refer to countries in which Islam is widespread, although there are no agreed criteria for inclusion. The term Muslim-majority countries is an alternative often used for the latter sense.

Islam is the second-largest religion in Europe after Christianity. Although the majority of Muslim communities in Western Europe formed recently, there are centuries-old Muslim communities in the Balkans, Caucasus, Crimea, and Volga region. The term "Muslim Europe" is used to refer to the Muslim-majority countries in the Balkans and the Caucasus and parts of countries in Eastern Europe with sizable Muslim minorities that constitute large populations of indigenous European Muslims, although the majority are secular.