What is "d-flat major"

a. (context music English) describing a piece, song, or scale that has a D-flat major key n. (context music English) a major key with five flats with the notes D♭, E♭, F, G♭, A♭, B♭, C

D-flat major is a major scale based on D-flat, consisting of the pitches D, E, F, G, A, B and C. Its key signature has five flats.

Its relative minor is B♭ minor. Its parallel minor, D♭ minor, is usually replaced by C♯ minor, since D♭ minor features a B in its key signature and C♯ minor only has four sharps, making it rare for D♭ minor to be used. C♯ major, with seven sharps, has a similar problem. Therefore, D♭ major is often used as the parallel major for C♯ minor. For example, in his Prelude No. 15 in D-flat major ("Raindrop"), Frédéric Chopin switches from D-flat major to C-sharp minor for the middle section in the parallel minor, while in his Fantaisie-Impromptu, primarily in C-sharp minor, he switches to D-flat major for the middle section for the opposite reason. Ferdinand Ries' third concerto likewise switches to D-flat major for a while for the return of the second theme in the first movement. Claude Debussy also switches from D-flat major to C-sharp minor in the significant section in his famous Clair de lune. Antonín Dvořák's New World Symphony likewise switches to C-sharp minor for a while for the significant section in the slow movement.

D-flat major is enharmonic to C-sharp major. In music for the harp, D-flat major would be preferable, not only because harp strings are more resonant in the flat position, but also because modulation to the dominant key is easier (by putting the G pedal in the natural position, whereas there is no double-sharp position in which to put the F pedal for G-sharp major).