Grouping

Specify how or if you want the Grouping field to be populated, you can specify the source and the maximum number of genres you want to add. Genres are added to a single field allowing all genres to be search for within one field, the grouping field is often used in iTunes as a way of supporting multiple genres for a song.

Warning:this field was originally for storing Classical music works and since iTunes 12.5.3 is now used for this again for MP3 and AIF formats, if you have Classical Music in your collection you should think carefully before using this option for grouping genres.