Muhajir is an Arabic word, widely used in the Muslim world that refers to someone who has emigrated from one place to another. In particular, it refers to the early Muslims, companions of Muhammad, who emigrated with him from Makka to Medina in the wake of the Hijra, as opposed to the Ansar, or Madinan Muslims of the time.

Muhajir or Mohajir is essentially an ethnic group within Pakistan. Muhajirs are Urdu-speaking people who originally emigrated from India to Pakistan during the partition of 1947. While Muhajirs form what amounts to an ethnic group within Pakistan, the group is actually comprised of people from different ethnic groups and regions in India, such as Uttar Pradesh, Bihar, and Hyderabad. They are united by the Urdu language.

Muhajirs are spread throughout Pakistan, with large populations in Karachi. In Karachi especially, they have occasionally been involved in ethnic strife with local groups such as the Sindhis. Most Muhajirs who originally immigrated to Pakistan were relatively more educated than most of their Pakistani counterparts, and as such they have generally held more positions in the government and amongst the professional class. This has also caused friction with the Punjabis, ethnic group that comprises the majority of Pakistan's population.

In Turkey, the term muhajir (Turkish muhacir or maacir) corresponds to people whose ancestors emigrated from the Balkans. After the end of Ottoman rule (especially after 1878 and 1912), a large portion of Muslim population took refuge in Turkey. Today, the word, having lost its original meaning ("an immigrant"), refers to someone who has Balkan ancestry.