“Memorial Day…observed on the last Monday of May, honoring the men and women who died while serving in the U.S. military. Memorial Day 2021 will occur on Monday, May 31.
“Originally known as Decoration Day, it originated in the years following the Civil War…. By the late 1860s, Americans in various towns and cities had begun holding springtime tributes to these countless fallen soldiers, decorating their graves with flowers and reciting prayers.
“Memorial Day became an official federal holiday in 1971.”
From https://www.history.com/topics/holidays/memorial-day-history