Once known as “Decoration Day”, Memorial Day is a time for remembering the people who died while serving in America's armed forces.
A History, from the US Department of Veterans Affairs:
Three years after the Civil War ended, on May 5, 1868, the head of an organization of Union veterans — the Grand Army of the Republic (GAR) — established Decoration Day as a time for the nation to decorate the graves of the war dead with flowers. Maj. Gen. John A. Logan declared that Decoration Day should be observed on May 30. It is believed that date was chosen because flowers would be in bloom all over the country.
The first large observance was held that year at Arlington National Cemetery, across the Potomac River from Washington, D.C.
The ceremonies centered around the mourning-draped veranda of the Arlington mansion, once the home of Gen. Robert E. Lee. Various Washington officials, including Gen. and Mrs. Ulysses S. Grant, presided over the ceremonies. After speeches, children from the Soldiers’ and Sailors’ Orphan Home and members of the GAR made their way through the cemetery, strewing flowers on both Union and Confederate graves, reciting prayers and singing hymns.