Generally, if there’s only one album of music from a movie, it’ll be referred to as the soundtrack. The album of music from A New Hope has always been titled Star Wars - Original Motion Picture Soundtrack, up to and including the most recent reissue, which was May of last year.
But if a movie gets two or more albums of music, it generally gets separated into the orchestral score, which will be titled as such, and one of songs played in the movie, which might be original, or might be existing songs featured in the film. And in some cases where they really want to sell two records, the soundtrack will have songs not featured in the movie, but are similar in style, genre and/or tone to ones in it.
So, for example The Crow had two soundtrack albums. One was titled as the original score, and is just orchestral music composed by Graeme Revell. The other, titled Original movie Soundtrack is a compilation of punk, metal, goth and industrial songs, all of which appeared in the movie. Some of these, such as Big Empty by Stone Temple Pilots were also on albums the bands had put out themselves; while others such as Burn by The Cure and Nine Inch Nails’ cover of Dead Souls were recorded specifically for the album, and didn’t appear on any other album.
by comparison, The Matrix also has two soundtrack albums. Again, one is an original score with music by Don Davis, the other is a compilation of 13 rock, metal, dance and industrial songs. But only 8 of them are in the movie, with the other 5 just being similar in tone, or by bands popular with people who liked songs in the soundtrack (there’s Marilyn Manson and Rob Zombie songs in the movie, so the soundtrack pads out the run length with Rammstein and Ministry)