Memorial Day is observed on the last Monday in May to commemorate the men and women who have died while in military service.
Originally known as Decoration Day, a time for the nation to decorate the graves of the war dead with flowers (first held three years after the end of the Civil War), the date of May 30 is believed to have been chosen because flowers would be in bloom across the country.
By the end of the 19th century, Memorial Day observances were being held across the nation. In the year 2000, Congress passed and the president signed into law “The National Moment of Remembrance Act,” encouraging all Americans to pause at 3 p.m. local time on Memorial Day for a moment of silence to remember and honor those who died in service to our nation.
Info from: U.S. Department of Veterans Affairs