In movie industry terminology, a sound track (two words) or just track is an audio recording created or used in film production or post-production. Initially the dialogue, sound effects, and music in a film each has its own separate track (dialogue track, sound effects track, and music track), and these are mixed together to make what is called the composite track, which is heard in the film. A dubbing track is often later created when films are dubbed into another language.
The contraction soundtrack (one word) came into use with the advent of so-called "soundtrack albums" in the early 1950s. First conceived by movie companies as a promotional gimmick for new films, these commercially available recordings were labelled and advertised as "music from the original motion picture soundtrack." This phrase was soon shortened to just "original motion picture soundtrack." More accurately such recordings are made from a film's music track, because they usually consist of the isolated music from a film, not the composite (sound) track with dialogue and sound effects.
Soundtrack has since come to denote three different things: the recorded sound accompanying a visual medium such as a motion picture, television show, or video game, just the music in it alone, or a genre of music ("soundtrack music" or "soundtracks").
The abbreviation OST is often used to describe the musical soundtrack on a recorded medium, such as CD, and it stands for Original Soundtrack; however, it is sometimes also used to differentiate the original music are heard and recorded versus a rerecording or cover of the music.
The term soundtrack now most commonly refers to the music used in a movie (or television show), and/or to an album sold containing that music. Sometimes, the music has been recorded just for the film or album (e.g. Saturday Night Fever). Often, but not always, and depending on the type of movie, the soundtrack album will contain portions of the score, music composed for dramatic effect as the movie's plot occurs. In 1908, Camille Saint-Saens recorded the first music specifically for use in a motion picture (L'assasinat du duc de Guise), and releasing recordings of songs used in films became prevalent in the 1930s. Henry Mancini, who won an Emmy Award and two Grammys for his soundtrack to Peter Gunn, was the first composer to have a widespread hit with a song from a soundtrack.
By convention, a soundtrack record can contain all kinds of music including music "inspired by" but not actually appearing in the movie; the score contains only music by the original film's composer(s).
Soundtrack may also refer to the music used in video games. While sound effects were nearly universally used for action happening in the game, music to accompany the gameplay was a later development. Rob Hubbard and Martin Galway were early composers of music specifically for video games for the 1980s Commodore 64 computer. Koji Kondo was an early and important composer for Nintendo games. As the technology improved, polyphonic and often orchestral soundtracks replaced simple monophonic melodies starting in the late 1980s and the soundtracks to popular games such as the Dragon Quest and Final Fantasy series began to be released separately. In addition to compositions written specifically for video games, the advent of CD technology allowed developers to incorporate licensed songs into their soundtrack. (The Grand Theft Auto series is a good example of this.) Furthermore, when Microsoft released the Xbox in 2001, it featured an option allowing users to customize the soundtrack for certain games by ripping a CD to the hard-drive.
Only a few cases exist, of an entire soundtrack being written specifically for a book.
A soundtrack for J. R. R. Tolkien's The Hobbit and his trilogy The Lord of the Rings was composed by Craig Russell for the San Luis Obispo Youth Symphony. Commissioned in 1995, it was finally put on disk in 2000 by the San Luis Obispo Symphony.
For the 1996 Star Wars novel Shadows of the Empire (written by author Steve Perry). Lucasfilm chose Joel McNeely to write a score. This was an eccentric, experimental project, in contrast to all other soundtracks, as the composer was allowed to convey general moods and themes, rather than having to write music to flow for specific scenes. A project called "Sine Fiction" has made some soundtracks to novels by science fiction writers like Isaac Asimov and Arthur C. Clarke, and has thus far released 19 soundtracks to science-fiction novels or short stories. All of them are available for free download.
The 1985 novel Always Coming Home by Ursula K. Le Guin, originally came in a box set with an audiocassette entitled Music and Poetry of the Kesh, featuring three performances of poetry, and ten musical compositions by Todd Barton.
In comics, Daniel Clowes' graphic novel Like a Velvet Glove Cast in Iron had an official soundtrack album. The original black-and-white Nexus #3 from Capitol comics included the "Flexi-Nexi" which was a soundtrack flexi-disc for the issue. Trosper by Jim Woodring included a soundtrack album composed and performed by Bill Frisell.
Many audio books have some form of musical accompaniment, but these are generally not complex enough to count as a complete soundtrack.