I don't know what that is. I don't want to know what that is.
"Festivus" is a pseudo-holiday made up by the father of one of the writers on the sitcom Seinfeld. The "holiday" made its way into the plot of a 9th season episode, probably the closest the show ever got to a "holiday episode."
The holiday eschews the religious aspects of other holidays this time of year and the commercialization of Christmas (the genesis of the holiday in the back-story in the episode.) The holiday, generated by George Costanza's father Frank, is fairly mean spirited as it involved lashing out at loved ones and eventually fighting them.
In the wake of the episode it's taken on a tongue-in-cheek form of celebration also probably as a form of "revolt" against the religious/commercialization of other holidays this time of year. It's a holiday everyone can enjoy.
Bullet points of the holiday:
1. The ornamental centerpiece is a 6-foot aluminum pole with no adornments. (Of note. In a recent holiday display "protest" someone erected a pole made one of beer cans along a nativity scene and menorah.)
2. "The Feats of Strength." In the episode the holiday isn't "over" and no one may eat until someone has wrestled the host of the dinner and has him pinned.
3. "Airing of the Grievances." In the episode it's common during the holiday dinner to shout at loved ones the ways they've let you down over the past year.
4. "Festivus Miracle." Though created by Kramer it's "part" of the holiday as celebrated by fans. Usually by exclaiming normal, mundane but coincidental occurrences as "miracles."
No gift exchanges required and no traditional meal. (The Costanzas were having meatloaf and spaghetti.) It's just a fun little "holiday."
Local radio station has an "Airing of the Grievances" inspired by the show (including sound clips from the episode in the bumper-music for the segment) every Friday during the last hour of the program where callers call in and air a grievance which is noted with little to no argument from the hosts.