It is so called because under the older Julian calendar, Christmas Day celebrations fell on that day whereas under the Gregorian calendar it falls on December 25.
It is the traditional end of the Christmas season and the last day of the Christmas holidays for both primary and secondary schools in Ireland.
In the Scottish Highlands the term Little Christmas (Scottish Gaelic: Nollaig Bheag) is applied to New Year's Day, also known as Là Challuinn, or Là na Bliadhna Ùire, while Epiphany is known as Là Féill nan Rìgh, the feast-day of the Kings.
The Transalpine Redemptorists who live on Papa Stronsay celebrate 'Little Christmas' on the twenty-fifth day of every month, except for December, when the twenty-fifth day is of course celebrated as Christmas Day.
In some parts of England, such as Lancashire, this day is also known as Little Christmas.
In Norway and Sweden, Little Christmas Day refers to January 13 (Norwegian: Tyvendedagen; Swedish: Tjugondedag), twenty days after Christmas, and is regarded as the day when ornaments must be removed from Christmas trees and any leftover food must be eaten.
Somewhat confusingly Christmas Eve is also referred to as "Little Christmas" in Scandinavia.
In the Isle of Man, New Year's Day on January 1 was formerly called Laa Nolick beg in Manx, or Little Christmas Day, while January 6 was referred to as Old Christmas Day.
The name Little Christmas is also found other languages including Slovene (mali Božič), Galician (Nadalinho), and Ukrainian.
In other parts of the world, it is sometimes referred to as Old Christmas or Old Christmas Day, so called for the same reasons as in Ireland, in that this was the traditional day of celebration under the Julian calendar.