incidental music. Mus. written for atmospheric effect or to accompany the action in a play. It was provided ‘incidentally’ as far back as Gr. drama. Purcell wrote much incidental mus. for the th. of his day, and there are dozens of superb examples since the early 19th cent., e.g. Beethoven's for Goethe's Egmont, Mendelssohn's for Shakespeare's A Midsummer Night's Dream, Grieg's for Ibsen's Peer Gynt, Bizet's for Daudet's L'Arlésienne, Fauré's and Sibelius's for Maeterlinck's Pelléas et Mélisande, Walton's for Shakespeare's Macbeth, etc. Music for films and TV is also in a sense ‘incidental music’.

in·ci·den·tal mu·sic • n. music used in a film or play as a background to create or enhance a particular atmosphere.