Which of the following is NOT a U.S. holiday?

Super Bowl Sunday is considered a culturally significant event in the United States as it revolves around the annual championship game of the National Football League (NFL). However, it is not recognized as an official U.S. holiday. In contrast, Martin Luther King, Jr. Day, Presidents' Day, and Labor Day are all federally recognized holidays that citizens can observe with various commemorations and time off work. These holidays serve to honor important historical figures, events, or social movements, whereas Super Bowl Sunday, while popular, is primarily associated with sporting activities and entertainment rather than a formal public observance.