The Solemnity of Mary, the Holy Mother of God is a feast day of the Blessed Virgin Mary under the aspect of her motherhood of Jesus Christ, whom Christians see as the Lord, Son of God. It is celebrated by the Latin Rite of the Catholic Church on 1 January, the Octave (8th) day of Christmastide.
The feast is a celebration of Mary’s motherhood of Jesus. The English title “Mother of God” is a translation of the Latin title Dei Genetricis, which means “She Who Generated God”, as the corresponding Greek title Θεοτόκος (Theotokos) means “She Who Gave Birth to God”. This title was dogmatically adopted at the First Council of Ephesus as a way to assert that Jesus is God, and that his mother can therefore be called Mother of God. The title that the 1 January feast celebrates is thus not only Mariological but also Christological.