What is the X in X-mas?
A notion introduced by Florentin Smarandache whereby the probability of some event is more than one. Tautological probability is used for universally true propositions, i.e. those which do not depend on time, space, subjectivity, etc.
[Florentin Smarandache, "A Unifying Field in Logics. / Neutrosophy: Neutrosophic Probability, Set, and Logic", American Research Press, Rehoboth 1999].