Catholicos is a title used in the Armenian Orthodox Church to refer to the head bishop. However, there are many different titles across different Christian denominations that can be used interchangeably with Catholicos. In the Eastern Orthodox Church, the equivalent title is Patriarch. In the Catholic Church, the equivalent title is Pope. In the Assyrian Church of the East, the equivalent title is Catholicos-Patriarch. In the Indian Orthodox Church, the equivalent title is Catholicos-Metropolitan. In the Ethiopian Orthodox Church, the equivalent title is Abuna. These titles all refer to the head bishop or leader of the respective denomination, with Catholicos being specific to the Armenian Orthodox Church.