A requiem is a religious ceremony performed for the dead. A requiem, or dirge, can also be a piece of music used for this ceremony or in any other context honoring those who have died.
The word requiem comes from the opening words of the Roman Catholic Mass for the Dead, which is spoken or sung in Latin (requies means “rest”). In a nonreligious context the word refers simply to an act of remembrance. Mozart, Brahms, and Dvořák have all written important requiems. The English composer Benjamin Britten wrote his famous "War Requiem" for the reconsecration of a cathedral that was destroyed in World War II.