A temp track is an existing piece of music or audio which is used in film production during the editing phase. It serves as a guideline for the mood or atmosphere the director is looking for in a scene.
The track is usually replaced before release by an original soundtrack composed specifically for the film. While some feel that having to follow a temp track can be limiting for a composer, it can be a useful tool in finding the right style of music for a particular scene and can be a time-saver for both the composer and director.
The temp track is sometimes also referred to as scratch music, temp score or temp music.
References
Temp track Wikipedia(Text) CC BY-SA