Christmas Lemmings is a series of short computer games released between 1991 and 1994, based on the original Lemmings game released in 1991. First released as Xmas Lemmings as two four-level demos in 1991 and 1992, there were two later full retail releases on the Amiga, PC, and Macintosh in 1993 and 1994.
The gameplay remains exactly the same as the original Lemmings game, requiring the player to lead the required number of lemmings to their exit by giving them the appropriate "skills". The original game Lemmings is not required to play any of the Xmas Lemmings games.
The difference between these games and the original game are the Christmas/snow-styled graphics of the levels, and that all the Lemmings wear Santa Claus suits.
Source: Wikipedia, "http://en.wikipedia.org/wiki/Christmas_Lemmings," available under the CC-BY-SA License.