From Longman Dictionary of Contemporary Englishtheme music/song/tunetheme music/song/tunemusic or a song that is often played during a film or musical play, or at the beginning and end of a television or radio programme the theme song from ‘The Brady Bunch’ → theme
Examples from the Corpus
theme music/song/tune• Sometimes the cartoon theme song is better than some of the episodes themselves.• Tampons that play the Hollyoaks theme tune when inserted?• Gowie Corby, Gowie Corby, the theme tune for all that's wrong in this school.• I know she liked the theme music.• I worked on the theme song with Ziggy Marley.• The theme music for the show starts up.• The theme music starts and I immediately find something more interesting to do.• The theme tune from Titanic was played at their wedding. 