This is an invented holiday - somewhat like a lot of them throughout the year.
I just love the episode on Seinfeld - like so many others.
As I researched, there is even a website dedicated to all things Festivus - Festivus.com
If you are thinking about celebrating Festivus - here are the rules.
If you know nothing about Festivus, it was started by Frank Costanza (George's dad) because he couldn't get George the doll he wanted for Christmas & had become fed up with the commercialization of Christmas.
(I am chuckling as I read & write, this seems like a good way to purge all the toxic craziness that has plagued us all year - we need to vent that out too!)