Source music is any music in a TV show or film that seems to be emanating from a tangible, physical source within the scene. For instance, the song playing in a disco or honkytonk; music that seems to be coming from a jukebox; or the song heard when a character puts a CD in his or her stereo, switches on the car radio, or puts on the headphones from an iPod. Source music can also be an actual performance, such as a band playing on a stage.
Placing this kind of music is typically the easiest way to break in. It’s much easier to get 12 seconds of your song in the background of a TV show than to get Rihanna or Tim McGraw to record it.