Definition of "theme song" []

• An often repeated song in a musical play that is identified with the work or one of its characters. (noun)
• A song that is identified with a performer, group, or radio or television program. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "You can almost hear Britney singing that bump-and-grind Pepsi theme song in the background: The rrrride!"
• "A jaunty, upbeat song featuring Stevie Wonder's uplifting harmonica playing, the single didn't make much of an impact on the charts (it's two week stay peaked at #13), but found success as it seemed destined to be the theme song to the new millennium."
• "Suddenly Bessie, grim-eyed, set up the languishing theme song of a film."