A playlist is a list of Playlist Tracks that you can select to play along with your slideshow. A playlist track is a Soundtrack that is associated with fade in and out effects and volume values. The First Playlist is by default associated with the first slide in the slideshow. This playlist is always linked to the first visible slide in your slideshow, until the playlist is renamed.
Playlists are useful for saving a particular list of songs, along with their fade in and out effects, and their volumes.
The transition effect used to change from one playlist tracks to the next, is the fade effect.