Muhacir (sometimes maacir in colloquial Turkish) is a term of Arabic origin (مهاجر, Muhajir or Mohajir) in Turkish language, used across ethnicities, and that corresponds to people whose ancestors migrated from formerly Muslim territories (Dar al-Islam in Islamic terminology), considered lost to the non-Muslims (Dar al-harb): the Balkans (Balkan Turks, Gajals, Albanians, Bosniaks), Caucasus (Abkhazians, Ajarians, 'Circassians', Chechens), Crimea (Crimean Tatar diaspora), Crete (Cretan Turks) or Africa (Sudanese Mahdists, Algerian partisans of Emir Abdelkader).
Muhajir (or mohajir, from Arabic muhajir, Albanian spelling muhaxhir), in Albanian-populated regions including Albania and Kosovo, refers to Albanians from Chameria (Greece) and parts of Vilayet of Kosovo (Sanjak of Nis, Sanjak of Yenibazar etc.) which were ceded to Serbia and Montenegro. They were deported through the ethnic cleansing exercised by the Greeks and Slavs beginning the weakening of the Ottoman Empire.
Muhajirism was emigration of Muslim indigenous peoples of the Caucasus into the Ottoman Empire following the Caucasian War (in the last quarter of the 19th century). During this mass movement, hundreds of thousands Muslims left Russia. "Muhajir" (Arabic: مهاجر) is an Arabic word meaning refugee, immigrant or emigrant.