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 could in fact have been 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)