Santa Claus was a folklore figure from certain Earth cultures, typically associated with the Christmas season.
In 2154, while analyzing Xindi data, Charles Tucker suggested in frustration that the data may in fact be a letter to Santa Claus, rather than anything important. (ENT: "Countdown")
In 2371, a Santa Claus figure was included in Jean-Luc Picards nexus experience of Christmas with his family. (Star Trek Generations)