The Answer:

Chrismukkah, to the extent that it exists, is a hybrid holiday combining Christmas and Hanukkah. (It should be noted that Chrismukkah is, at this point, more of a concept and an attitude toward the holiday season than a bona fide holiday of its own.)

While the concept is not a new one—according to Ron Gompertz, author of Chrismukkah: Everything You Need to Know to Celebrate the Hybrid Holiday, German Jews celebrated "Weihnukkah" in the 1880s, with the German name for Christmas being "Wehnnachten"—it unquestionably rose to prominence in 2003 through its inclusion on the popular TV show The O.C. Characters on the show have continued to celebrate Chrismukkah every year, and the term has caught on among others around the country.

There are several factors that might account for the popularity of the Chrismukkah concept. One might be a backlash against the increasing politicization of the holiday season, with people taking umbrage at tidings of "Merry Christmas" or "Happy Holidays." The term seems to cry out "can't we all just get along?" Another might just be an indulgence in postmodern mashup fun. But perhaps the largest factor is the increasing prevalence of families with mixed religious heritages. Chrismukkah neatly solves the question of whether to celebrate Christmas, or Hanukkah, or both, or neither. Like mixed families themselves, it brings together elements of both worlds.

It's not surprising, then, that the very idea of Chrismukkah has been decried by many in both the Christian and Jewish communities. Both see it as something of a perversion, equating two holidays with fundamentally incompatible themes. Whether this is a problem, or precisely its appeal, is a matter of perspective.

—The Fact Monster