Memorial Day is an American holiday, observed on the last Monday of May, honoring the men and women who died while serving in the U.S. military. Memorial Day 2019 occurs on Monday, May 27.
Originally known as Decoration Day, it originated in the years following the Civil War and became an official federal holiday in 1971. Many Americans observe Memorial Day by visiting cemeteries or memorials, holding family gatherings and participating in parades. Unofficially, it marks the beginning of the summer season.
More info can be found at https://www.history.com/topics/holidays/memorial-day-history