The "Ride of the Valkyries" refers to the beginning of act 3 of Die Walküre, the second of the four operas constituting Richard Wagner's Der Ring des Nibelungen.
As a separate piece, the "Ride" is often heard in a purely instrumental version, which may be as short as three minutes. Together with the "Bridal Chorus" from Lohengrin, the "Ride of the Valkyries" is one of Wagner's best-known pieces.