Music that we often barely hear is called "background music". The person here is obviously trying to use "foreground" as the opposite, meaning that the music is more obvious. I've never heard the word used this way before.
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Newguestyou don't want too much foreground= You don't want the kind of music that draws attention to itself. The music must not be so interesting, rhythmic, loud, or colorful in other ways that it distracts attention from what it is intended to accompany as a background.