Memorial Day is a United States federal holiday observed on the last Monday of May (May 25 in 2015). Formerly known as Decoration Day, it commemorates U.S. men and women who died while in the military service. First enacted to honor Union soldiers of the American Civil War (it is celebrated near the day of reunification after the Civil War), it was expanded after World War I.
Many people observe this holiday by visiting cemeteries and memorials. A national moment of remembrance takes place at 3 p.m. local time. Another tradition is to fly the flag of the United States at half-staff from dawn until noon local time. Volunteers often place American flags on each grave site at National Cemeteries.
Members of the Veterans of Foreign Wars take donations for poppies in the days leading up to Memorial Day; the poppy's significance to Memorial Day is the result of the John McCrae poem "In Flanders Fields."
In addition to remembrance, Memorial Day is also used as a time for picnics, barbecues, family gatherings, and sporting events. One of the longest-standing traditions is the running of the Indianapolis 500, an auto race which has been held in conjunction with Memorial Day since 1911. The Coca-Cola 600 has been held later the same day since 1961. (From: Wikipedia, license: CCA-SA)