Theotokos (/ˌθiəˈtɒkəs/; Greek: Θεοτόκος, transliterated Theotókos) is the Greek title of Mary, the mother of Jesus used especially in the Eastern Orthodox, Oriental Orthodox, and Eastern Catholic Churches. Its literal English translations include God-bearer and the one who gives birth to God. Less literal translations include Mother of God. Roman Catholics and Anglicans use the title Mother of God more often than Theotokos. The Council of Ephesus decreed in 431 that Mary is Theotokos because her son Jesus is one person who is both God and man, divine and human.
Read more about Theotokos: Etymology and Translation, Theology, Use in The Early Christian Church, Third Ecumenical Council, Hymns, Solemnity, Icons