Also called Decoration Day. a day, May 30, set aside in most states of the U.S. for observances in memory of dead members of the armed forces of all wars: now officially observed on the last Monday in May.
any of several days, as April 26, May 10, or June 3, similarly observed in various Southern states.
used in a general sense is from 1830s; as a specific holiday commemorating U.S. war dead (originally Northern soldiers killed in the Civil War) it began informally in late 1860s. officially from 1869 among veterans' organizations.