Complex sentence: Festivus is a parody holiday popularised by the American sitcom "Seinfeld", celebrated on December 23, which has since become a secular celebration, serving as an alternative to participating in the pressures and commercialism of the Christmas holiday season.
Split into simpler sentences: Festivus is a parody holiday popularised by the American sitcom "Seinfeld", celebrated on December 23. It has since become a secular celebration which serves as an alternative to participating in the pressures and commercialism of the Christmas holiday season.