What does 'Xmas' stand for?

Christmas

Who was chained to a rock where an eagle devoured his liver daily? Who betrayed Samson’s secret to the Philistines? Who portrayed Dr. Evil in the "Austin Powers" movies? Who played Dr. Derek Shepherd, known as McDreamy, in "Grey's Anatomy"? Who ruled Prussia as an enlightened monarch noted for military victories and reforms during the mid-18th century?