Whether you love or hate the “Seinfeld” finale — and a lot of fans really hate it — the ninth and final season of the show about nothing was crucial for one big reason: the introduction of Festivus.

Festivus is an anti-commercialist holiday celebrated on December 23, popularized by a 1997 "Seinfeld" episode. The holiday was based on a real family tradition started in the 1960s by the father of ...