Memorial Day, originally called Decoration Day, is a day of remembrance for those who have died in service of the United States of America. Regardless of the exact date or location of its origins, Memorial Day was borne out of the Civil War and a desire to honor our dead. It was officially proclaimed on May 5th 1868 by General John Logan. The first state to officially recognize the holiday was New York in 1873 and is now observed in almost every state on the last Monday in May
On the first Decoration Day, General James Garfield made a speech at Arlington National Cemetery, and 5,000 participants decorated the graves of the 20,000 Union and Confederate soldiers buried there.
The dictionary says this about the term memorial. It is something designed to preserve the memory of a person. It is Intended to commemorate someone or something such as a memorial service in the dead man's honor. And one of the synonyms for the concept is remembrance.