"All Parts" indicates a single-track, which is the 4-part equal recording within the multi-track package. At only $1.99 each, single tracks, or "All Parts", were developed to provide an inexpensive way to hear the entire song, just in case the sample does not allow you to make sure it is a match for your arrangement.
If you purchase the full learning media set, or the multi-track package, the "All Parts" is included and should not be purchased separately, except for the use indicated above. Full, multi-track package costs range from $20.00-$60.00, depending upon the age of the title and the number of tracks.
Please note that Kim's learning media is for educational purposes only and includes neither arrangements nor arrangers fees that are required for performance of the songs you select.