soundtrack

Short definition from Wiktionary

Noun

1. 1
   A narrow strip running down a movie film that carries the recorded sound in synchronization with the pictures.
2. 2
   The sound (especially the music) component of a movie, video game, etc.
3. 3
   A recording of such music for sale.
4. 4
   A background sound that is part of a larger event.

Verb

1. 1
   To provide, or to act as the sound or music component of a film.