Festivus is celebrated on December 23 every year and was described in Seinfeld as a holiday against the commercialism of Christmas.
Festivus came from the the holiday memories of Seinfeld writer Dan O'Keefe's holiday memories. His father, had decided to celebrate Festivus with his family in the mid-60's, according the Festivus website.
While the Festivus Pole (a pole of aluminum unadorned by tinsel or decorations) was made up for the show activities like the Feats of Strength (which includes a wrestling match between family members) and the airing of greivances really happened at the O'Keefe household.
Since the Seinfeld episode, people have picked up on the humorous holiday and starting celebrating it. You can find the instructions of how to have your own Festivus celebration as well.
Have you or would you ever celebrate Festivus? Let us know in the comments below.