Sit nomen Dómini benedíctum
Ex hoc nunc, et usque in sæculum
Blessed be the Name of the Lord
from this time forth for evermore
The Feast of the Holy Name dates back to the 15th century, when it was celebrated, usually in conjunction with the Feast of the Circumcision on 1 Jan. Under Jewish law, a child would have been named on the day of his circumcision - and thus, this feast celebrates the naming of Jesus on the day of his circumcision.
In modern times, the date of this celebration varies, with some Church's celebrating it on the 3rd of January, others on the first Sunday of the New Year unless that Sunday falls on the 1st, 6th or 7th, in which case it is celebrated on the 2nd Day of January.
In Medieval times, this would have been a continuation of the celebrations of the twelve days of Christmas, but there would be no specific saint or event to whom the day was universally dedicated - i.e., to put it in the latin, feria. That said, many localities then, as now, would have had their own specific celebrations.
Happy Tenth Day of Christmas