A soundtrack is a recorded audio signal accompanying and synchronised to the images of a book, drama, motion picture, radio program, television program, or video game; colloquially, a commercially released soundtrack album of music as featured in the soundtrack of a film, video, or television presentation; or the physical area of a film that contains the synchronised recorded sound.

In movie industry terminology usage, a sound 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, 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. This is also known as an M&E (music and effects) track. M&E tracks contain all sound elements minus dialogue, which is then supplied by the foreign distributor in the native language of its territory.

Current dictionary entries for soundtrack document soundtrack as a noun, and as a verb. An early attempt at popularizing the term sound track was printed in the magazine Photoplay in 1929. A 1992 technical dictionary entry in the Academic Press Dictionary of Science and Technology does not distinguish between the form sound track and soundtrack.

The contraction soundtrack came into public consciousness with the advent of so-called soundtrack albums in the late 1940s. First conceived by movie companies as a promotional gimmick for new films, these commercially available recordings were labeled and advertised as "music from the original motion picture soundtrack", or "music from and inspired by the motion picture." These phrases were 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 isolated music from a film, not the composite (sound) track with dialogue and sound effects.

The term original soundtrack (OST), often used for titles of albums of soundtrack music, is sometimes also used to differentiate the original music heard and recorded versus a rerecording or cover version, and behaves as a unique type of concept album that revolves around a unified theme in a story.

Types of soundtrack recordings include:

The soundtrack to the 1937 Walt Disney animated film Snow White and the Seven Dwarfs was the first commercially issued film soundtrack. It was released by RCA Victor Records on multiple 78 RPM discs in January 1938 as Songs from Walt Disney's Snow White and the Seven Dwarfs (with the Same Characters and Sound Effects as in the Film of That Title) and has since seen numerous expansions and reissues.

The first live-action musical film to have a commercially issued soundtrack album was MGM's 1946 film biography of Show Boat composer Jerome Kern, Till the Clouds Roll By. The album was originally issued as a set of four 10-inch 78-rpm records. Only eight selections from the film were included in this first edition of the album. In order to fit the songs onto the record sides the musical material needed editing and manipulation. This was before tape existed, so the record producer needed to copy segments from the playback discs used on set, then copy and re-copy them from one disc to another adding transitions and cross-fades until the final master was created. Needless to say, it was several generations removed from the original and the sound quality suffered for it. The playback recordings were purposely recorded very dry (without reverberation); otherwise it would come across as too hollow sounding in large movie theatres. This made these albums sound flat and boxy.