September 12 is currently the optional memorial of the Holy Name of Mary in the General Calendar of the Roman Rite.
The celebration was removed from the General Calendar during the 1970s, but was reinstated by St. John Paul II in 2003.
According to the Catholic Encyclopedia, "After the siege of Vienna and the glorious victory of Sobieski over the Turks (12 Sept., 1683), the feast was extended to the universal Church by Innocent XI, and assigned to the Sunday after the Nativity of Mary."
This means that it had one of the highest ranks, being celebrated on a Sunday.
By the early 20th century, the celebration of the Holy Name of Mary was moved to September 12, which is the anniversary day of Sobieski's victory. At this time it was given a third rank, which is similar to the designation of memorial in today's liturgical calendar.
This assignment to September 12, eight days after the birth of the Virgin Mary, corresponds to the feast of the Holy Name of Jesus, which is celebrated eight days after the birth of Jesus.
The feast of the Holy Name of Jesus is connected to the Jewish ceremony of circumcision, which was celebrated eight days after a boy's birth and is recorded in the Bible.
Girls do not have the same naming ceremony in Jewish tradition, though girls are named within the first few weeks of birth.
While the celebration of the Holy Name of Mary isn't a major feast on the current calendar, historically it was a very important liturgical commemoration.
