It's Festivus, the completely made-up holiday that seems to have taken on a life of its own. We actually celebrate this in my family - actually, we celebrate my parents wedding anniversary (today is their 48th!), but since Seinfeld declared December 23 Festivus, that's what we now call it.
To answer several questions -- no, we do not air grievances or indulge in the feats of strength - but we do open gifts, make a delicious meal and generally engage in holiday festivity.
Due to the popularity of Seinfeld, and the sheer fact that Americans will find any excuse to buy new shit, there are now places to buy Festivus Poles, as well as a litany of books about the "holiday." Whatever. All I know is, it's the holiday season - go get some.
And while you're at it, if you are so inclined, go take this Festivus quiz over at Mental Floss.
Happy Festivus, y'all!