What's the main difference between a "theme song" and a "soundtrack?"

Native speaker’s answer
Rebecca
Good question! A "soundtrack" is a recording of the music from a movie. Whereas a "theme song" is a song usually played at the beginning of a show, is signatory, or one that is known for and related to the name of the movie it's in. For example, the theme song for the movie, "Beauty and the Beast" is called "Beauty and the Beast." Ex: I love the "Friends" theme song. It's so catchy that I never skip it. Ex: The Wizard of Oz is known for the theme song "Over the Rainbow" in its soundtrack.