You say "background music"!

The term background music refers to minimally intrusive music as you can hear in a lift or a restaurant, for example.

Background music is also called background sound or room music.

For many people, the term "background music" is just another term for a soundtrack, a sound layer or a composition accompanying a TV program, a film, a business or family video, an advertizing, a presentation...

Although it often goes undetected, background music can nonetheless play an effective role to create an ambience, evoke a specific feeling, guide a narrative...

Illustrative music can be considered as background music, even if the first holds a prominent place in the narrative.
We prefer to use the term "music composition"!