Isn't that true of most holidays pretty much anywhere in the West these days? Sure, there's Christmas and Halloween and Easter that have specific themes, but excepting deeply-religious communities who practice associated traditions, they're as meaningful as cosmetic items in free-to-play games. But every country has a bunch of other holidays that most people don't know or care about much beyond knowing it's a day off.

Do you mean April?

That holiday is May Day but it's not federally recognized in the US specifically to hinder labor organizing in this country. President Grover Cleveland went with the September alternative proposed by one of the early unions because it was "less inflammatory" than May Day which was preferred by all the other unions.