What is "music drama"

Music drama \Mu"sic dra`ma\ An opera in which the text and action are not interrupted by set arias, duets, etc., the music being determined throughout by dramatic appropriateness; musical drama of this character, in general. It involves the use of a kind of melodious declamation, the development of leitmotif, great orchestral elaboration, and a fusion of poetry, music, action, and scene into an organic whole. The term is applied esp. to the later works of Wagner: ``Tristan und Isolde,'' ``Die Meistersinger,'' ``Rheingold,'' ``Walk["u]re,'' ``Siegfried,'' ``G["o]tterd["a]mmerung,'' and ``Parsifal.''