Christmas is an Earth-made event celebrated throughout the entire planet on 25 December every Earth-year.
When going to Atlantis in 2006, Lt. Colonel Cameron Mitchell told Vala Mal Doran that Dr. Daniel Jackson was so excited about going there, he felt excitement reminiscent of that felt by a kid staying up all night on Christmas Eve. (SG1: "The Pegasus Project")
When trapped in a time dilation field for 50 years on the Odyssey, SG-1 celebrated Christmas at least once. The decorations that were present were likely created using the Asgard computer core. (SG1: "Unending")
While trying to return to Destiny in 2010, Lt. Matthew Scott's team arrived on a planet, where it was snowing. Chloe Armstrong mentioned that it reminded her of when she used to spend Christmas in a cabin in Vermont. (SGU: "Lost")