James Newton Howard

[Weirded Wonder]

The main difference between soundtrack music and score is this.
A score is the original music composed for the film to back the action and what have you. Think of all the music for Star Wars, Indiana Jones, etc. A soundtrack is usually the music for a film that is not written for it. The rap music in How High, or the 50s music in American Grafitti.

This does not mean that something Bruce Springsteen wrote for Philadelphia is not score material. It was written for the film in mind but not really composed to fit in any particular place in the movie.

Queen's Flash Gordon soundtrack is a great example of the best of both worlds.